In the context of melee combat, this question is essentially about called shots
One of the main pitfalls of combat mechanics that target specific parts or elements of the enemy is that if the PC's can do it then NPC's and Monsters can do it too. Is everyone in your campaign willing to play in a world where their weapons, armor and spellbooks are constantly being destroyed?
I think it's worth investigating the melee combat aspect of this question in the context of called shots, about which many questions have been asked and thoroughly answered on this site. I suggest you run a site search for called shots [dnd-5e] to find all the called shots discussions tagged as dnd-5e.
I don't want to restate what has already been stated on this site numerous times, so here's a link to a great discussion aiming at specific body parts. The top answer by @christutty nails some of the main pitfalls of allowing called shots, and the other answers also cover important aspects of allowing called shots.
- Don't do it
- The mechanics can bog down game play
- Tit for tat (if PC's can do it, all their opponents can too)
- Mechanics need to be such that relative level and ability are still a factor (can a 3rd level ranger essentially take out a high level enemy with one arrow?)
- There are other games that support this much better than DnD
- Makes players OP
- There is no RAW that support this
All these issues are as relevant to this question as they are to any called shot discussion.
Spells that target objects are built into RAW
There are certain spells that target objects and, unless they state otherwise, they can be used on objects being worn or held by another creature. One such spell that would be very useful in this situation is Chain Lightning (PHB 221). It would be up to your GM to determine what the DEX +/- for Morlock's spell component pouch would be, as well as potential bonuses based on being under partial or full cover behind your enemy's body. When targeting worn objects in combat I think these kinds of issues need to be resolved.
As a reference PHB 196 has a section on Cover. Basically:
- 1/2 cover = +2 AC / DEX
- 3/4 cover = +5 AC / DEX
- Full cover = cannot be targeted except by a spell with an area of effect.
I don't know of any RAW that discuss the natural DEX of a worn object, but I would call it as the same as the wearer.
Object HP, AC and other stats and considerations may also need to be resolved before a spell attack on a worn object. For example, you may also need to consider whether a defensive spell cast by the target also protects the object you are targeting on their person.