First Answer
You (3rd seat, unfavorable) are declaring. The opening lead is the six of clubs.
Repeat Question 1
Which card should you play from dummy? If West has the King and Queen, you should play the Jack. If West has the King-ten or Queen-ten, you should play the nine. If East has the King-Queen doubleton, you should play the five. Playing the nine gains in two of those four situations, so the nine is your percentage play.
Say that you play the nine, and East plays the Queen.
Should you win or duck?
Bonus from Val: If you are thinking that North overbid, I agree. In my opinion, relatively few 8 HCP hands are good enough to invite game opposite a 15-17 one notrump. When both hands are balanced, unless there is a five-card suit, I find that 25 combined HCP are not enough to provide a 50% (or better) chance for game.