♦3: You lead partner’s suit, Diamonds, giving count, so you lead the 2 or 3 according to your agreements. My advice: when partner opens 1♦, 1♥ or 1♠, give count. If the opening was 1♣, lead fourth best.
♣2: You know about a side-suit in dummy, Diamonds. Without any opposition in trumps or the side-suit, put a low Club on the table without hesitation, hoping you’ll establish enough tricks for your side.
♠3: In this sequence where North didn’t ask for majors and there is no other contraindication, it’s preferable to lead a major. Lead the Spade 3, fourth best. Reminder: against No-Trump contracts, in order to lead the Queen from Queen-Jack, you need at least the 9 as well.
♦3: 5♠ asks for a control in the suit of the opponent’s pre-empt. 6♥ confirms a first-round control. This means the only chance to beat the contract seems to be to get one trick in Spades and one in Diamonds. Don’t waste time and lead a Diamond.