At Coxwell, clearly at Mortimer, with Toronto East hospital there.
With Pape, you've got all this density around Cosburn .. so if you put one entrance at Cosburn, and the other end of the platform with an exit to Torrens, your close enough to O'Connor.
Probably the same for Donlands as well, though with less density everywhere, I'd be tempted to put one extrance south of Cosburn, and the second as far to the south as feasible, between Memorial Park and Mortimer. Donlands is probably the one that isn't a no-brainer.