If my investigator has a clue token on his card and he is at a location does that mean that there is a clue token at that location or does the act of investing a location remove if from the table all together. Like Roland’s gun says +2 fight if there is a clue at the location so does that mean if he has a clue on him and he is in the location does that count as a clue at your location

If an investigator has a clue, it is not at his location. To be at a location, it needs to be on the location card (or next to it or wherever you put it)

I believe if you look at the faq, its in there.

"A card ability that refers to clues "at a location" is referring to the undiscovered clues that are currently on that location." - please see in the rules reference, under 'clues': https://arkhamdb.com/rules#Clues (the only time a clue is 'at' a location is, as @Jobu said, when it's on the location card itself. Not on enemies, not with investigators or their cards, just the location itself).