Alright, for those who are having trouble finding this feature, here's a screenshot I just took, at the TBT screen:
When you move your mouse over the relevant area the mouse cursor will increase in size and the tooltip text will pop up. I do run RFB, but I don't think that has any sort of effect on what's happening here. Also note, I am running the game at 1600x1200 resolution, so the exact spot you find the tooltip popup may vary.