Hillary tweeted right away: "SCOTUS's decision is a victory for women in Texas and across America. Safe abortion should be a right—not just on paper, but in reality. -H" and "This fight isn't over: The next president has to protect women's health. Women won't be 'punished' for exercising their basic rights. -H" And Trump hasn't tweeted anything. Josh Voorhees (at Slate) says "The obvious answer is that Trump is either unwilling or unable to quickly sum up his thoughts on a topic that he has expressed so many conflicting views on in the past and that has caused him so many problems in the present...."
Another obvious answer is: Gender politics isn't his thing. He only talks about abortion when pushed or when attacked.