OR, cny, it might be a front chainring. With the 42T middle ring on my triple, I tend to run a lot in the middle ring and all over the cassette. So I replace the middle ring about twice as often as the cassette. So it's one or the other. When you stand on the pedals to make it skip, look down at the chainring. You'll see it jump if it's that. If you don't see it jump, then you need a new cassette.

If it's the cassette, the other thing you can do is put the old chain back on and run it until it breaks (carry a master link). Cheaper that way. I've a friend who puts on 40K miles/year. He has sets of two-cog "cassettes", chainrings, and chains, all stretched and worn to match. When one component gets too worn to work with the others, he just moves it to a different component set. That many miles, and pristine equipment starts to run into money. Because he replaces all but two cogs with spacers, he doesn't have the problem of the chain skipping on some cogs and not others.