I have a quest with an optional objective of training with Giraud Gemane, but I just realised I don't know how to detect this.

I found the info where the PC requests training, and I can override this, although I'd prefer a less invasive approach. I'd also like something that let's me detect if the player actually paid for training, rather than just looking at the menu and saying "HOW much!?!"

Current plan is to add another info to the training topic, just above Guraud's current one with an added condition that my quest be running and at the correct stage. Then I can check the actor value before and after and complete the objective if the value went up.

I'd prefer not to touch vanilla topics at all though. Anyone got any better ideas?

OnTrackedStatsEvent("Training sessions") plus a check to see if you're in the Bard's college, maybe? But it won't give the amount you paid.

That sounds like an improvement. I don't mind how much they pay as long as it isn't zero.