Today I was surfing in Reddit, and found a quote:
The saddest people always try their hardest to make people happy because they know what it’s like to feel absolutely worthless and they don’t want anyone else to feel like that. - Robin Williams
What I wondered was the clause in the sentence: "what it's like to feel worthless". In English, we usually see a clause like what is a dog, in which the word what is the subjective pronoun of the sentence sth is a dog, but the clause mentioned above doesn't seem to be following this rule because it has a subject "it" in it.
I thought that what is probably a determiner for "it" — say, for example "what kind of dog is the biggest breed."— but I found there's a interrogative sentence like "What is it like to be a nurse", so my assumption of what as a determiner seems to be false.