I doubt the Sanhedrin has either religious or political Jurisdiction and authority to Judge a Christian, a head of state and a Pontiff.

 As to their claims the palestinians stole their land obviously one has to suppose they have proof of this? otherwise they can reportedly be sued by them for slander and damages?

Regarding their claim of antisemitism because the Vatican refers to Palestine as a nation? in my humble opinion I think a first year law student could throw this claim out the window based, as I see it , in its seemingly  lack of any legal foundation to support this claim if one refers to what is legally defined as antisemitism, it would seem that recognizing Palestine as a nation does not appear to fit the definition. And lets not forget Palestinians are semitic .

Why should we worry about what they think?

Since they summoned him, perhaps he should go.  

It would be a chance for him to try his hand at the New Evangelization.

Although I think the New Evangelization is to help those who are "sacramentalized" and does not include prosletyzing to outsiders.

Cardinal Kasper said that Vatican II did away with all that returning nonsense.

UPDATE:
BREAKING ISRAEL NEWS
A recent Breaking Israel News article about the nascent Sanhedrin’s intention to put Pope Francis on trial in absentia for his recognizing the Palestinian state has caused quite a ruckus. Though it may seem shocking to many that a group of rabbis would interfere in international policy, or exert authority over the Pope, the Sanhedrin feels compelled to do so. Rabbi Dov Stein, the secretary of the Sanhedrin, explained to Breaking Israel News that he feels it is their duty to bring God’s law into this world.
Thus far, the Vatican has not responded to the Sanhedrin’s letter. “As expected, no.  It would seem that the Pope has chosen to ignore the letter. But a trial will be held anyway, and the result may be very risky for the Pope,” Stein said.
“God in heaven is listening and obeys the Sanhedrin because the Torah interpretation is in the hands of the Sanhedrin here in this physical world, not in the heaven in the hands of the angels.”
Not just a court for Jєωs, the rabbis on the Sanhedrin believe they are commanded by God to right injustice wherever it appears, regardless of religion or country.
“It has happened in the past that people have ignored the Sanhedrin, which is a mistake, because the Sanhedrin is vital to the proper functioning of the world. Only when the Jєωιѕн nation will heed the Sanhedrin of the Torah, will the Torah be one. Today God’s Torah is not the same Torah for all the Jєωs. Our unity is damaged because of this, because of people ignoring the Sanhedrin,” Stein explained.
In just one example, the Sanhedrin held a trial in 2008 against the Chinese government having to do with the persecution of the Falun Gong. Followers of Falun Gong, a branch of Buddhism, approached the Sanhedrin in 2007, claiming that their fellow practitioners in China were being persecuted. The claims, which have since been substantiated by media sources, were that in 1999 the Communist Party leadership declared Falun Gong a “heretical organization” and began systematically persecuting them, with reported human rights violations.
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As of 2009, at least 2,000 Falun Gong practitioners had died as a result of abuse in custody. Some observers put the number much higher, and report that tens of thousands may have been killed to supply China’s organ transplant industry.
“The Chinese embassy tried to prevent it, but the Sanhedrin is not obligated to politics, only to justice,” Stein said. The Chinese embassy in Israel was contacted by the Sanhedrin and responded that the hearing would likely have a negative effect on the diplomatic relations between Israel and China.
Professor Hillel Weiss, a member of the Sanhedrin, responded, “If Armenian representatives would have approached me and complained about the Turks I would support opening a Sanhedrin trial against the Turks. Every regime needs to know that if it hurts another ethnic group it is committing a crime.”
In 2008, the Sanhedrin ruled against China. The Association for Asian research wrote about the judgement, “While many nations and institutions have stayed silent as to the persecution of Falun Gong, the Sanhedrin has gotten it right. It’s time for the world to respond.”
When asked what authority the Sanhedrin has to put foreign leaders and governments on trail, Stein explained, “The Sanhedrin is the Supreme Court with responsibility for the world. All of the people of the world should at least be following the Torah, even if it is only the Seven Laws of Noah, (which are incuмbent on all non-Jєωs). The interpretation of the Torah in each generation is in the hands of the Sanhedrin.”
While the Sanhedrin’s actions of trying Pope Francis in absentia have proven controversial, Stein reveals that the court has received international support for its cause. “We have had many people contact us, Jєωs and Gentiles, and everyone was pleased with what we are doing and very supportive. They appreciate that there is now one true voice of the Jєωs and their Torah. There is not even one Beit Din (court) of Jєωs who dare to say the truth in the world,” he said.
When asked whether the government of the State of Israel has gotten involved, Stein stated, “I do not believe that they will support any such step. The opposite is probably true. The Israeli government is used to being pressured and attacked by the whole world, and therefore the government of Israel is afraid of every political shadow.”
With the Pope soon to address the United States Congress, the boundaries separating religion and state are becoming less clear. It is clear that many international conflicts today are driven more by religious fervor than by economic or diplomatic interests. It may just take a religious court to resolve the Injustices that plague and threaten humanity.

They can have him. He's theirs anyway..