One figure banded about is 95% but this was from a sample size of 128 people. The question also was not about being a Zionist but having "favorable views of Israel."

See here:

https://jewishcurrents.org/are-95-of-jews-really-zionists

"The Pew 2013 survey found that 69% of American Jews were somewhat (39%) or very (30%) emotionally attached to Israel, while 31% were not very (22%) or not at all (9%) attached. Eighty-seven percent of American Jews said that caring about Israel is either essential (43%) or at least important (44%) to what being Jewish means to them."

-In what way they were "attached" is hard to discern as Jewish mythology makes Jews "Israelites" or "Children of Israel" but I think we can discern from this and the rest of the Pew that amongst American Jews a majority support the idea of an Israeli state.