Thank you's from here: G2G, click on someones name, (this takes you to their G2G page), Then click on "## contributions, (this takes you to a page with a list of "So and So did something to Wikitree-ID, find where it says they answered a question. You can do this for other things, like if someone contributes to a profile you manage.
From here, I usually just say thank you, publicly, like you did.
Thank you for asking the question Joan. I'm always happy to help.