please it is urgent

[mr.ars]

what is the difference between?

Why doesn't he study?

Why does he not study?

[engee30]

what is the difference between?

Why doesn't he study?

Why does he not study?

The difference lies in the syntax only. The meaning is the same.

[David L.]

Why doesn't he study?

This is colloquial speech, with the contraction "doesn't".

Without the contraction, we don't write
"Why does not he study?"

It is, "Why does he not study?"

This has a very formal sense to it, and you will find the collocation 'why does he not...' , for example, when people are discussing literary works e.g.
Of Shakespeare's Measure for Measure: "Why does he not depend on his trusted counselor Escalus for advice and ..."

and serious discussions:
If God is all-powerful, why does He not just kill Satan?

[mr.ars]

thanks dears