As you now know, 3rd generation have a SA/DA action, earlier models have DAO. Therefore, you can determine 3G by checking which action type you have. One way you may do this is as follows:
1. Clear the chamber, ie remove the magazine, and retract the slide, looking into the chamber to make certain the pistol is unloaded.
2. Release (close) the slide. The pistol is now "cocked" (if it is a SA/DA 3rd Gen).
3. Now look carefully at the trigger, specifically how far rearward it's position is in the triggerguard.
4. Next, with the pistol pointed in a safe direction, dry fire it. This will serve to "decock" the pistol if it is a SA/DA.
5. After dry firing to decock the pistol, again look at the trigger's position within the triggerguard. It will be more centered than in step #3 above if it is a SA/DA (ie 3rd Gen). With the pistol pointed in a safe direction, again dry fire it. If it is not a 3rd Gen, and therefore a DAO, this trigger pull will feel identical to the one in step 4.
Hope this helps, and make certain to at all times observe safe firearm handling practices.