Many people posting here with no clue (the exceptions are also obvious). It doesn't make sense to see Jews as a homogeneous voting bloc. There are some quite different types of Jewish voters. It has been mentioned already, but 1990s Jewish FSU immigrants are often very strong Trump backers, especially people from non-Ashkenazi groups. And there are different types of non-immigrant, Ashkenazi voters too. That said, it is true that Trump is a very bad fit for most Jewish demographics.
I expect Trump to get something around McCain's 22%, probably slightly less.
I actually think that Cruz and Rubio would have done the best with the Jewish community.
No, Cruz would do terrible too (though not as bad as Trump). Even conservative Jews are generally not conservative in the same way as evangelicals are. Cruz represents a lot of things most Jews just can't relate to -- in certain ways much more so than Trump.