new JobApplying[MAX_PLAYERS]; // If you want PVars, don't create this variable

// on the /joinjob command, you'd have
JobApplying[playerid] = 2 // for drug dealer job

// or, if you want PVars, use it like:
SetPVarInt(playerid, "ApplyingJob", 2); // This creats a PVar ApplyingJob and sets it to 2.

// And now, the accept job command:

YCMD:accept(player, params[], help)
{
    #pragma unused help
    if(strcmp(params, "job", false) == 0)
    {
                if(JobApplying[playerid] == 0)
                         return SendClientMessage(playerid, -1, "You haven't apply for any job, so you can't accept it.");

   // OR if you use PVars, skip the previous step and do:
                if(GetPVarInt(playerid, "ApplyingJob") < 1)
                         return SendClientMessage(playerid, -1, "You haven't apply for any job, so you can't accept it.");

                   // And now, just set the players job to its variable
                   PlayerInfo[playerid][Job] = JobApplying[playerid]; // For normal variables
                   PlayerInfo[playerid][Job] = GetPVarInt(playerid, "ApplyingJob"); // For PVars
                  // And don't forget to reset the variable
                    JobApplying[playerid] = 0; // For normal variable
                    DeletePVar(playerid, "ApplyingJob"); // For PVars
}