Unless you changed to a new chain recently, it's probably not chain skip. Chain skip most often occurs when a new chain is installed on an old cassette. Chain skip means that the chain stays on the intended cog, but rides up over the teeth.

For an old chain to skip with a used cassette, it must have a large amount of elongation, in the 1.5-2% range.

The other things mentioned are not really chain skip, if the chain moves to another cog.

Worn chainrings cause chain suck, not chain skip.