look X. "what do you think about earth"?
Y. "I thik it is circle".
X. "how do think of its circleness? do you believe it is true?"
so,use "how" for check up someone's perseption of something!!
we use "what" while i am asking somethong for the first time! mean that to know what he/she think of it!!!!
after we heared someone's thinking towards someting, then,use "how" with pronouns such as "him", "it", "its" instead of calling the name of the person/thing that we asked about!!
what.... about +pronoun/possesive noun what do you know about Jack/him!
how.......of + possesive adjective+noun how do you think of his mother?
or X. what do you think about love,Mr Y?
Y. I think love is a backbone of life.
X. How do you think of it Mr Z?
Z. well, I have just a similar thinking wiht Mr Y.
so, "how" is usually used for contrasting someone's persepective with others towards someting!
What is normally used to know their understanding with out being expressed!!!
we can say "how do you think it?"