You can't check the mob level in that function. conlevel is passed in as a parameter, so you need to look at where the function is called. Assuming you're not in a group and you killed a mob it's called from NPC::Death()
Code:
int conlevel = give_exp->GetLevelCon(GetLevel());
if (conlevel != CON_GREEN)
{
if(GetOwner() && GetOwner()->IsClient()){
}
else {
give_exp_client->AddEXP((EXP_FORMULA), conlevel); // Pyro: Comment this if NPC death crashes zone
You can see where conlevel is calculated and passed there.