My own definition - proto-science is something put forward by someone who knows the scientific orthodoxy in the field, suggesting that some idea might be true. Pseudo-science is something put forward by someone who doesn't know the scientific orthodoxy, asserting that something is true.

Testing which category any particular claim falls into is in my experience relatively straightforward if you know the scientific orthodoxy already - as a pseudoscientist's idea will normally be considered absolutely false in certain aspects by those who know the orthodoxy. A genuine challenger to the orthodoxy will at least tell you that they know they are being unorthodox, and why - a pseudoscientist will simply assert something else without any suggestion that their point is even unusual. This is often the easiest way to tell the two apart.

If you don't know the orthodoxy, it's much harder to tell, but generally speaking pseudoscience can also be distinguished a couple of other ways.

Socially - proto-science advocates have a relevant degree on the whole, and tend to keep company of other scientists. Pseudo-science advocates often have a degree, but advocate a theory unrelated to it, and are not part of anything much.

Proof - pseudo-science appeals to common sense for proof, wheras proto-science only tries to explain rather than persuade. Pseudo-science can normally be explained perfectly well in English, wheras proto-science typically requires at least some mathematics if you want to understand it properly.

Both look disappointingly similar once they've been mangled by a poor scientific journalist - go back to the original sources if you really need to know!