How can i setup a hurt trigger which only damage zombies?

ent waittill( "trigger", who );
if(!IsPlayer( who )){
	//do this to ai
	who DoDamage( 50, ent.origin );
}

while(1){
	ent waittill( "trigger", who );
	ai = GetAiArray( "axis" );
	for( i = 0; i < ai.size; i++ ){
		if(ai[i] IsTouching( ent )) ai[i] DoDamage( 50, ent.origin );
	}
	wait(.5);
}

Use a trigger_muliple in radiant, get the ent in script and just waittill it is triggered, and then check if the ent that triggered it is not a player.

ent waittill( "trigger", who );
if(!IsPlayer( who )){
	//do this to ai
}

Depending on what you do, additional dog checks would be necessary

I would like to make a trap which kills zombies and dogs in higher rounds, but can't kill the player that fast.

Example:
A trigger hurt with dmg and damage 10000.
--> Can kill zombies in higher rounds, but also kill the player instantly.

So i need to reduce the player damage to example 25.

Thanks for your help so far

while(1){
	ent waittill( "trigger", who );
	if(IsPlayer( who )){
		if(who.health>21){
			who DoDamage( 20, who.origin );
		}else{
			RadiusDamage( who.origin, 10, 20, 20,1 );
		}
	}else{
		ai = GetAISpeciesArray( "axis", "all");
		for( i = 0; i < ai.size; i++ ){
			if(ai[i] IsTouching( ent )) ai[i] DoDamage( 50, ent.origin );
		}
	}
	wait(.5);//time between hurting
}

while(1){
	ent waittill( "trigger", who );
	players = get_players( );
	ai = GetAISpeciesArray( "axis", "all");
	allents = array_combine( players,ai );

	for( i=0;i<allents.size;i++ ){
		if(allents[i] IsTouching( ent )){
			if(IsPlayer( allents[i] )){
				if(allents[i].health>21){
					allents[i] DoDamage( 20, allents[i].origin );
				}else{
					RadiusDamage( allents[i].origin, 10, 20, 20,1 );
				}
			}else{
				allents[i] DoDamage( 50, ent.origin );
			}
		}
	}
	wait(.5);//time between hurting
}

Ok, I would do something like this then:

while(1){
	ent waittill( "trigger", who );
	if(IsPlayer( who )){
		if(who.health>21){
			who DoDamage( 20, who.origin );
		}else{
			RadiusDamage( who.origin, 10, 20, 20,1 );
		}
	}else{
		ai = GetAISpeciesArray( "axis", "all");
		for( i = 0; i < ai.size; i++ ){
			if(ai[i] IsTouching( ent )) ai[i] DoDamage( 50, ent.origin );
		}
	}
	wait(.5);
}

ai = GetAISpeciesArray( "axis", "all");
         for( i = 0; i < ai.size; i++ ){
            	if(ai[i] IsTouching( ent )) ai[i] DoDamage( 50, ent.origin );
 

ai = GetAISpeciesArray( "axis", "all");
         for( i = 0; i < ai.size; i++ ){
            	if(ai[i] IsTouching( ent )) ai[i] DoDamage( 50, ent.origin );
 

And i can change the 50 for example to 1000 to do more damage to the ai, right?

ai[i].health + 666

Yup, and I added more options. If you want to kill them, people usually do:

ai[i].health + 666