Sadly your product link is no longer working, but I am fairly sure you are talking about an adapter "3.5 mm TRRS plug to 2 × 3.5 mm TRS jack", of which one of the jacks is to plug in a microphone and one to plug in headphones. Basically it splits a notebook computer's combined TRRS audio jack into the components: one mic jack, one headphones jack.
In that case, the answer is pretty clear when looking at the pinout of the original TRS microphone jacks in computers, as that will be the pinout provided for the microphone jack of this adapter.
That microphone jack is a 3.5 mm audio jack with three terminals ("TRS") for an unbalanced mono signal. The pinout uses the consumer device microphone pinout, as follows:
- tip terminal: microphone signal
- ring terminal: supply voltage (+3 V to +5 V)
- sleeve terminal: ground
(Source is here; sorry, found only a good source in German.)
So, this is not a stereo microphone jack wiring. It is for ordinary mono microphones with a TRS jack. This microphones typically have the tip and ring connectors shorted together (source), leading to a microphone with a combined signal and voltage line (see "Tonaderspeisung" in German Wikipedia). That shorting also makes clear that such a microphone really needs only two terminals, and that's what it gets when connected to a TRRS audio jack in a computer.