I think of Newton, Hooke, Leibniz, Wren, Locke -- assuming they knew hard to believe they would not have thought it crazy but I have read nothing about Newton, et al saying anything.
As Stephen Burnap has already explained, it is unlikely that Newton would even have heard of the Salem Witch Trials.
As for Newton's personal beliefs on the subject of witchcraft, I think most people are now aware that Newton studied alchemy. As a result, there has been more interest in his belief, or otherwise, in "related", non-scientific subjects. Fortunately for modern historians, Newton wrote fairly extensively on subjects like the devil, demons, witchcraft, ghosts, etc., and it is therefore possible to trace his evolving views over time.
Stephen Snobelen, of University of King's College, Halifax, has explored this topic in some detail in his 2004 paper: Lust, Pride, and Ambition: Isaac Newton and the Devil (available to download as a pdf file from ResearchGate).
For now, it should be sufficient to repeat just one quote from Newton (that is included in Snobelen's paper):
"... to beleive that men or weomen can really divine, charm, inchant, bewitch or converse with spirits is a superstition of the same nature wth beleiving [sic] that the idols of the gentils were not vanities but had spirits really seated in them"
Thus, it is quite clear that Sir Isaac Newton did not believe in witchcraft. Had he heard of the events occurring in Salem in 1692/93, he would presumably have judged them on that basis.
It's a big assumption that they knew. At the time, Salem was the middle of nowhere, with a colony founded specifically to keep to itself. The trials themselves would likely not have attracted much attention, especially since witch trials were happening all through Europe during that period. In the 250 years before 1750, around 40,000 witches were executed
The Salem Witch Trials only became famous because they happened in a small place that ended up as a cultural core of a powerful country. Asking what Newton thought of the Salem Witch Trials is a bit like asking what Neil DeGrasse Tyson thinks about the a particular couple killed for homosexuality in Dubai.
As mentioned by Steven Burnap Salem was isolated, but we can have a look at other examples. During the witch processes in Stockholm 1678 Urban Hjärne (chemist, geologist, physician and writer) initially was for torture, but later changed his mind and realised it was a case of mass hysteria and not witchcraft. He still considered witchcraft a reality and that the devil existed and had such powers.