Okay, the most usual sense of the verb колоть means to break something into pieces with something sharp, like an axe or a knife.
The second meaning of the word is to painfully or lethaly poke somebody with something which has a sharp tip, like a needle or a knife. Here you need to be aware that колоть in this sense means that you used something in your hands to perfom the action. So if you say that: я кольнул его стрелой that would mean that you poke somebody with an arrow which was in your hand rather than shoot the arrow into somebody.
The third meaning is to inject something into somebbody such as an antibiotic or a drug.

As for your case, here the word is used in a figurative sense and the sense is the first one I wrote. The word here means to try to put someone under pressure by asking him searching cunning questions or by threatening, or by beating the someone up, well, by whatever means it takes, to make the someone to finally tell the truth even though they don't want to.