Q)
Must I Swap a card, can I Pass.
A)
No, you are not allowed to Pass. You must Swap a card OR Knock.

Q)
Must I Swap a card even after the second Knock.
A)
No, do not forget that even after the second Knock, you are allowed to Knock as well. This effectively means that you can Pass in this situation as a third (fourth or fifth) knock has the same effect as passing.

Q)
If I make the first Knock must I be the one to make the second Knock.
A)
No, you do not have to be.

Q)
Are you meant to take out any cards with only three players.
A)
No, the full 56 cards are shuffled each time and 9 cards are dealt to each player and 5 cards to the pool. It does not change with the number of players. It does mean that only 32 of the 56 cards are used in a three player game.
Scoring Examples
1 1 3 3 3 3 3 3 3
Scores: 1 + 0 = 1 point.

1 1 2 3 4 5 6 7 8
Scores: 1 + 0 = 1 point.

1 1 2 3 4 5 6 7 8
Scores: 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 = 36 points.

1 1 2 3 4 5 6 7 8
Scores: 1 + 2 + 3 + 0 = 6 points.

1 1 1 1 4 5 6 7 8
Scores: 1 + 0 = 1 point.