I am soliciting advice  for a friend to convince her that dating a non-catholic is dangerous. She is 20 yrs old , raised as a traditional Catholic. He is baptized but was never raised in the Faith. I speak from the print of view that dating is for preparation for marriage and they need to be practicing Catholics. Also, his conversion has the opportunity to be compromised, as in a false conversion, just to keep the relationship going. She thinks that we should give him a chance to convert while she keeps dating him.  I argue that the conversion needs to happen outside of the relationship. Please respond with your advice or your own or some else's experience. I would appreciate it that this would not turn into a critique of my view of dating or someone's response. Just how would you respond if someone approach you with this situation.

I agree with your view.  I don’t know how long they’ve been dating but it sounds like there is mutual interest and there’s been a handful (maybe more?) of dates.  Your friend needs to politely yet firmly insist that this gentleman start attending church with her and he must also decide (relatively soon) if he’s interested in taking classes with the priest to learn the Faith.  
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If he’s opposed to both of these, then there’s no future in the relationship.  If he’s open to (consistently!) going to church but he’s opposed to taking classes, then they need to have serious conversations about why he’s opposed.  If he’s unwilling to discuss this topic, then the relationship has no future.  I agree, the conversion must take place first, before any engagement and must take priority at all costs.  
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I could name 20+ situations that I know of where the Catholic (men and women) was trying to convert a non-catholic/novus ordo and in all the cases where the Faith was not a priory, the catholic (men and women) suffered emotional heartbreak because they allowed themselves to get invested too early.  And the non-Trad ended up waking away after a lengthy dating period.  
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This doesn’t even mention the HUNDREDS of cases which I’ve heard of where (and many I know first hand) where the couple actually got married but the “convert” wasn’t really serious and fell back into their old ways and the Trad (and their children) are left with a cross to bear for the rest of their lives.  (Again, this has happened to both men and women I know).
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It’s a crazy dating world out there.  Be careful whom you date and be VERY CAUTIOUS and PRAY MUCH for God’s will.  Emotions can, and do, lead us astray in this area.  

Marriage is a risk.  Risk can be mitigated.  Taking a foolish and unecessary risk in whom you choose to marry has big consequences on your temporal and eternal happiness and your childrens' souls.  The effects of a poor decision will likely be around long after you are dead.

The goal of any person considering more than their immediat emotional state should be to marry a practicing and sincere (devout) Catholic.  Anything less than that is a risk.  There may be exceptions, but you should have very strong reasons for them.  Detached people should see the sense in those arguments.  If they cannot agree, then you are convincing yourself.

I've driven a car for 42 years without any serious accident or collison.  I could therefore have gotten away without even wearing a safety harness.  I have worn a safety harness 99% of the time when I drove a car or was a passenger.  When I began driving there was no legal requirement to wear one.  Some automobiles did not have them fitted in 1977.

Marriage is a risk.  Risk can be mitigated.  Taking a foolish and unecessary risk in whom you choose to marry has big consequences on your temporal and eternal happiness and your childrens' souls.  The effects of a poor decision will likely be around long after you are dead.

This.

Is this couple ever alone? If yes I don’t see how they are not sinning. Even if both are trads , if left alone they are in danger. I have 2 young daughters and have brought up the idea of chaperoning to my wife and others (non trads) and am looked as someone coming from another planet. I have a few more years to work on convincing my wife and kids but this will definitely be the biggest battle of my life as my wife is not as traditional as I

I agree that it is unwise to marry when one is of no desire for catholicism.  Maybe  see it this way:  one believe that 1 plus 1 is 2, the other believes otherwise.  Dr. David Allen White former of the Naval Academy had to teach or unteach student who were taught/brain washed of relatism. He said, you can not build bridges when all those involved have or believe different measures and such.

A marriage is a business, and you can not raise children, discipline and such when spouses are not on the same page.  Very risky.

I argue that the conversion needs to happen outside of the relationship. Please respond with your advice or your own or some else's experience. I would appreciate it that this would not turn into a critique of my view of dating or someone's response. Just how would you respond if someone approach you with this situation.

Well, conversion really does not need to happen outside of the relationship, but as it is, she should be well aware that he shows a definite sense of urgency to sincerely convert, if not, she had better get out while the gettin's good.

There was a girl in a very similar situation, she ended up marrying him, he fooled everyone including himself I think, everyone thought he was a good Catholic husband and father, well, it took about 12 years or so, but it ended up being fatal for her. He didn't murder her, she was 36 years old and died of a massive heart attack brought on by the sheer stress of trying to raise children as she was raised as she had to deal with everything you can imagine and worse that goes along with one raised trad, married to a fraud trad man.

Thankfully the children were taken away and raised by the God Parents, but that situation is terrible for the spouse who is determined to keep the faith while married to one without it. For your friend, in this day and age she is completely out numbered, if she makes it, it will surely be against all odds.