I like what I see.
I know that the tide is turning.
I've met the man who won the lottery.
(Not all agree this is a noun clause. See Note on the right.)
Compare the three examples above to these:
I like cakes.
I know London.
I've met Madonna.
that the tide is turning is replaced by London what is this I can't understand
I strongly advise you to avoid the term 'noun clause'. It's a misnomer that serious grammarians do not use. I realise that GM uses that term, but most of what GM says is wrong!
(1) "I like what I see / cakes."
(2) "I know (that) the tide is turning / London."
(3) "I've met the man who won the lottery / Madonna."
In (1) the similarity between "cakes" and "what I see" is that they are both noun phrases that have the same function, i.e. direct object of "like" (note that "what I see" can be paraphrased as "the thing I see").
(2) is trickier. Although "that the tide is turning" and "London" are different structures (the former a declarative content clause, the latter a noun phrase as direct object), the similarity between the two is that they are both complements of "know". Note that direct objects are a type of complement.
In (3) the similarity between "Madonna" and "the man who won the lottery" is that they are both noun phrases with the same function, i.e. direct object of "met".
In grammar, a content clause is a subordinate clause that provides content implied or commented upon by its main clause. The term was coined by Otto Jespersen. They are also known as "noun clauses".
You clearly know very little about English grammar, as is evident from the fact that you don't even know the difference between a noun phrase and a clause!
I'd explain why you're wrong, but judging by the above and your past replies on this site, I doubt if you'd understand a word I said.
The only accurate bit in your reply is that Otto Jesperson was responsible for the term 'content clause'. Note that he could have, but didn't, use the term 'noun clause', a misnomer if ever there was one.