I was thinking of a noun clause in which the relative pronoun 'that' can be the subject of the clause. I couldn't think of one. I found this website in which a lot of examples are made when a 'that clause' is a noun clause.
What I don't understand is the function of 'that' in aforementioned that-clauses! For example the relative pronoun 'who' in
'I know who did it'
is the subject and in
'I know who you should meet'
is the object. What's the function of 'that', let's say, in
'I know that he's a fraud'
If it's the subject of the clause, then what is 'he'?
Another example would be
That he's a fraud scares me!