[Abagail]

Its not hard if you know what your doing, and have all your checkpoints in a variable to store things. For instance,
when you set a CP for a player, maybe you can have a system with checkpoint IDS. For instance use a variable CheckPointID for players.
Ex:

pawn Code:

if(CheckPointID[playerid] == 0)

Or another option is checking for the closest coordinates where checkpoints are set throughout your game-mode, how-ever I wouldn't recommend this option.