Hi Shahbaz,
According to your question, I agree with Sam Sung that you can find the difference and distinguish these technologies looking at their recommendations series G.98x made by ITU-T. I am listing them here for your convenience: GPON – G.984.1; WDMPON – G.982; TWDM – G.989.2. In general, the main difference is channel multiplexing schemes and techniques (without the usage of any amplification in their transmission path). Let me know if you have any further questions.