The 6 digits/alphanumeric PNR number you refer to is completely different from fare basis. When you book online on TG.com you will be able se the fare basis (you need to click in the menu list in the right side of the screen to see the fare basis).

But in general all the cheap non-refundable (and often non-changeable) TG fares are in W or V class, often called TG saver or value fares. Q class or higher are more expensive TG fares (to some extent flexible) but are hardly worth the additional payment to get a few miles/points if W or V class is available.