Is a woman`s neck an Awrah (private part)?

All Perfect Praise is due to The Lord of The Worlds.

It is an Awrah, and it is forbidden for her to reveal it before non-Mahrams (Marriageable men). And Allah Knows Best.

Is it permissible for someone to make a supplication to Allah to marry an already married, or an engaged woman?

No, it isn`t, and the person who does so is sinful before Allah, The Almighty.

Does an internal examination require ghusl?

Ghusl isn't required for making internal examination; however, it invalidates one's fasting. And Allah Knows Best.

Who is "the poor" entitled to receive Zakah (obligatory charity)?

The poor is the one who has neither money nor a source of living, or has either of them, but it isn`t sufficient such as being in need for a hundred/JDs, and having an income of forty/JDs only.