1) In the clan chat list, there should be a yellow box with arrows on the right hand side of the list. Click on the arrow to "Show options". The far right option is "Check how much resources this clanmate has produced since the last build tick".
Note: You'll need to be on the same world as the member you are checking on.
If they have not visited, you'll get
2) If your members have their RuneMetrics set to "Public", visiting & capping at the citadel will show on their activity report. One of our clan members runs a report that pulls from all of our members' RuneMetrics pages to see who has and has not visited or capped each week.
Don't ask me how, I haven't a clue. It's possible that he's using the
Clan discord bot