is there a way to figure out a trunking system (freq, talkgroups, etc,)?
This question sounds a lot like "can you tell me what is wrong with my car?". In other words, more details are needed in order to correctly answer your intended question.
Is the trunked system Motorola, EDACS, LTR or something else? How one would go about figuring out a system depends first on which type it is. Some scanners can report the data you are looking for, and in other cases software running on your computer connected to a scanner may provide the information. Knowing which scanner(s) you are using would help us provide a better answer.
Finding all of the frequencies being used can be quite a task since some are hardly used. but perhaps you only need the control channel frequencies. Modern scanners only need the control channel frequencies for some types of trunked systems.
Do you want to know the talkgroup numbers, or do you want to know who is using them? Finding the active numbers is not too tough, but learning what they are used for takes either some 'inside' information or a lot of listening.
Is there a way? Yeah there are lots of ways. It all depends on what you exactly want to do, what you're monitoring with and what you know about the system already.