You can't. It's not in the game for the player character to wear, unfortunately. I don't know why. The customization options are extremely lazy in this game - it's the same 15-20 pieces of gear recoloured to create a sense of variety. These Trauma Team vests? They're the same for militech - just slapped some paint onto it and put the name "Trauma Team" onto it. Really wish they bring more apparel options in the future, cause as of right now, they don't want you to have the ability to completely cover your face in something - even the balaclavas are open-face and you can't combine glasses/visors with masks cause they take up the same slot. Can only imagine the possibilites if CDPR added all these masks/helmets/headsets from Arasaka/Militech/TT/MaxTac goons. Can't even cover yourself in armor without looking like a clown, cause the pieces that do drop from, say, Arasaka goons do not match anything we got in the game right now. I don't even think it would be a difficult task, seeing as how all they have to do is use the existing models and maybe slap some paint on them just to make them look different from the original. So many pieces the NPCs are wearing that I wish V could wear as well - I can only hope CDPR reads these forums and will add stuff like this somewhere down the line.