About responding to someone's gemlog, I've tried 3 things:

Sending an email or private msg on Mastodon or Twiter
If it's a long and kind of anonymous answer, I'll create a 'Re:' in my own smol.pub. With some luck a chain of linked posts create a conversation
Or if it's more to having replies, writing here on midnight works well, I think.

Replies

I do the same; if it's something I kind of want to be part of a public conversation, I create a Re: on my gemlog, update my own feed, and push my feed to Antenna. If it's reasonably personal, or not of general interest, I email.