[Joe Staff]

I'm assuming you're keeping a variable per player with kills and deaths.

OnPlayerDeath(playerid,killerid,reason)
{
Kills[killerid]++;
Deaths[playerid]++;
new string[100];
format(string,sizeof(string),"Kills:%d -- Deaths:%d",Kills[playerid],Deaths[playerid]);
TextDrawSetString(KillsDeathsText[playerid],string);
format(string,sizeof(string),"Kills:%d -- Deaths:%d",Kills[killerid],Deaths[killerid]);
TextDrawSetString(KillsDeathsText[killerid],string);
}