Which is pin 2 on a Harwin Datamate connector?
By far, most connectors of this type put the odd-numbered pins on one side and the even-numbered pins on the other, so the answer would be that pin 2 is below pin 1 in this drawing. The reason for this is that this type of connector is often used in conjuction with ribbon cable, and this makes the numbering in the cable sequential.

However, I have seen rare exceptions to this, where pins 1 to N/2 went down one side, and the rest down the other. If you can see the board silkscreen, see if there are any clues indicating whether this might be the case.

If you are designing a new board with this connector, of course, the final answer is entirely up to you.