Trump is a nationalist. His motto is "Make America Great". He doesn't appear to be into multiculturalism. This makes many Jews nervous.
Don't know why Jews would be scared of Trump. Do they not know that his now famous daughter, Ivanka, IS JEWISH as well as her husband and Trump's son-in-law, along with their 3 children? If Trump was any bit anti-Jewish or anti-Semite, I doubt his son-in-law and daughter would be out vigorously campaigning for him.
Also, Trump has been famous and a big shot in NYC for 40 years now and if he was racists or anti-Semitic, it would have come out long age.