You haven't said what you're trying to do, and the error tells you that p doesn't have a field called "jitem".
Perhaps what you are trying to do is to extract a member from a structure dynamically: that is, jitem is the *name* of a struct member, only known at runtime? In that case, you can use the Reflect package:
But that's really ugly and I think you should avoid it if at all possible. Go is not Python.
There are safer and simpler approaches, for example:
If all you're trying to do is pretty-print JSON, then encoding/json can do that for you:
or you can use a YAML library.