Playing the OC at the moment I have a problem disarming traps I never had before.
There´s a trap on a chest I´m not able to disarm - the DC is way too high. Simply triggering the trap with my buffed (elemental resistance) character outright killed him on several tries.
Is there any way to trigger this trap with my henchman, summoned monster etc. ? Sort of let it die but the trap is gone ? I´m not able to find any command to accomplish this.

One thing you could try is bashing it with a missile weapon. It helps if you use ammunition which deals elemental damage when you do so. Area of effect spells like Fireball, or certain specific ones like Ray of Frost and Flame Arrow may work as well.
However, the chest may be invulnerable to damage entirely.

In that case, you'll need to use a Find Traps spell or buy Thieving Tools. Alternatively, get a rogue for a henchman or use a pixie familiar.
In the event that the DC is still too great, triggering it is indeed the only way to disarm it. You can do this with possessed familiars, or indeed with characters under the effect of Constitution buffs, granted Temporary Hitpoints and under the effects of an energy protection spell. If you're desparate to get at it, die and use the respawn option.

Still, some traps won't disarm after being triggered. If you're facing one of these stuck on an indestructable chest, you need someone with a good disarm skill around.

If you are playing the OC and you just can't disarm it, then either bash it with a missle weapon as above, or recruit Tomi Undergallows to do it, then go back to what ever the safe haven portal location for which ever chapter you are doing and drop him off. If the chest turns out to be locked too, then he can unlock it once it is disarmed.

If you haven't been using Tomi up to then, have him level up before trying the chest. If they haven't been adventuring along with you as your character levels up, then the henchmen don't level up, but you can initiate conversation and somewhere along the conversation tree there will be the option to tell him to level up (to your characters present level). That way Tomi will have enough skill points to handle a high DC trap and lock.

I always used Tomi or Sharwyn to remove traps for me. Tomi was an expert for such, especially after I downloaded a patch which let me get into his inventory. I found that giving him thieves' kits didn't always work, but making sure he had belts of dexterity on him DID. nothing wrong with having "Halfling Death" do all your dirty work for you. Word to the wise, always equip your henchmen better than yourself if you are sending them into dangerous situations all the time.