Dear Br Dimond.
A protestant invites me to attend a lecture on creation by another protestant this Friday. It's not in any protestant temple and there's no religious service. If there's no praying together, can I attend it? Thanks
Yes, we don’t see any reason why you couldn’t go unless attacking the Catholic Faith is somehow an integral part of his presentation on Creation (which we highly doubt). You should at least try to convert the Protestant who invited you, of course, if you haven’t done so already.