[Sinner]

pawn Код:

if(isPlayerAdmin(playerid) {
    // Player is an RCON admin
}

OR, if you want to check for all the players in-game (post #2 is wrong code)

pawn Код:

for(new i=0; i<MAX_PLAYERS; i++) {
    if(isPlayerAdmin(i)) {
        // Player i is RCON admin
        // Add them to a string, or print their name or w/e here
    }
}