My little boy didn't point for ages. Was getting quite worried as he didn't seem to be interested in any form of communication - wasn't talking, wouldn't do signs, didn't point, didn't wave etc. As far as I could see, after lots of talking to others and worrying (!) this seemed to be down to two things (1) he's a very chilled out little chap and was perfectly content without communicating, and (2) I was generally anticipating his every need before he got bothered enough to point or indicate in any other way that he wanted something, partly because he was so laid back.
Started asking him if he wanted his cup rather than just giving it to him, and trying to demonstrate conversation, and waiting for a response. Also, giving choices and getting him to point to what he wants, and then hopefully try and say the word too (recommended by speech therapist) e.g. do you want apple or banana? do you want the car or the train?
He's now 3, and much better at saying what he wants .. "I want .." is one of his favourite phrases now! His speech is still a bit behind other children, but there doesn't seem to be an actual problem (been assessed by various professionals).
You don't say whether your son is trying to talk at all. Does anything above sound like him? If he's not trying to communicate at all, like my little one wasn't, it might be worth going to a speech and language drop-in if you have one near you. Ours are run through the local Sure Start Children's Centre.
Does he point at things in books? You could try actually holding his hand to show him what you mean when you say "Point to the train" or "Show me the car". (Be consistent about whatever phrase you use.) Took my son ages to do that too, but there's nothing wrong with his intelligence or learning or observational skills. He either didn't get it or simply didn't want to for some reason. He's great on his colours now, and loves learning his numbers. Recognises a few letters too.
Hope this is helpful.