1 - Place your CTI at the beginning of your clip in your sequence
2 - Match frame (F)
3 - in your source monitor, your original footage should be loaded at the exact same frame than your speed adjusted footage
4 - check the timecode associated with that frame
You can see TIMECODE if you use overlays (spanner icon in programme / source monitors). No way of viewing FRAMES there though.
You can get a TIMECODE list of source ins/outs if you export an EDL.
But, having played around with the timecode generator effect, I may be seeing the problem you have... it does not correctly reflect the source frame numbers of speed adjusted clips in either 'clip' or 'media' mode (it also affects the underlying frame shown in a speed change - which is surely a bug)
You'll probably be best trying to find an XML parser that will give you the information you want.
(Avid is much better if you need to deal with frame numbers.)