If today is Monday,..then does "This Monday" refer to today or the following Monday?
So ambiguous, Geo, hardly anybody would say it. Like you suggest, we'd better say "Today"
...referring to the following [coming] Monday... one could simply just say "This following Monday" or "Next Monday"
Both ambiguous, equivocal, yet used by everyone at all times, one of my pet peeves
"Two Mondays from now" would be best, but nobody says it this way
If it's Sunday we might say "a week from tomorrow," but if it's Saturday all bets are off