What particular diplomatic and economic issues does the king of Alashiya want to take up with the ruler of Egypt?

The purpose of the Wilmot Proviso was to prevent the spread of slavery to any territory won from Mexico during the war.

powers  are  denied  to the  national governmentin three distinct ways: some  powers, such as the  power  to levy duties on exports or prohibit the freedom of religion, speech, press, or assembly, are expressly  denied  to the  national government  in the  constitution.