1)
What is "Vakbuk"?
1.
Rashi: It is a flask. Malbim - refer to 19:10:1:1.
2)
Why does it say "Yotzer Cheres"?
1.
Rashi: It is of a potter, and it is of earthenware. Radak - the Targum reverses the words (a pitcher of earthenware, from a potter). The prefix Mem is omitted. We find like this - "Elchanan ben Dodo Beis Lechem" (Shmuel II, 23:24) is like mi'Beis Lechem.
2.
Radak: It is one who makes earthenware pots. Some flasks are of wood or of glass or metal.
3)
Why does it mention elders of the nation and of the Kohanim?
1.
Rashi: Take them with you. Radak - this is so that you will tell them the Nevu'ah. You will break it in front of them (verse 10), so it will be a wonder to them.