Sorry, you just said some new stuff to me, but I've never heard that Asus released notebooks in G750 or G751 series with TB2.
All of them were with TB1 I think. And now the new series with TB3 using a USB Type C connector.
Why are you asking for TB2? What made you asking such question? Why does this matter to you anyway?
For eGPU use I can tell you that I've stumbled into some issues with my laptop, don't know if the root cause was from thunderbolt adapter (Sonnet Echo express) or video card (GTX 680) or the laptop itself (G750JW).
Too see the Thunderbolt VEN\VID I think you need to connect something to it, otherwise it will stay hidden.
You can also raise the palm rest and look what is written on the chip.