A seminar about women in STEM fields
I have been to seminars like that, including ones where large numbers of my colleagues are present.

So long as you have meaningful and productive questions (i.e. don't ask a question for the sake of asking one) and ask them as respectfully as you would any other topic, there isn't a problem.

I will note that choosing not to attend is also sending a message, and in the seminar I was in, a number of colleagues expressed disappointment that the room was nearly entirely women (in this case it was about the status of women in the field).