Do you mean in general? In which case you're looking for ones that have 'sturdy', 'infused' etc as part of the description.
Or do you mean how do you know which you've already researched and which you need to research? In which case if you're on PC I'm sure there's probably an add on that'll tell you, if you're on console I don't think there is anything (I don't remember ever seeing anything anyway). I went old school and used pen and paper to keep a track of what traits I've researched.
If you join an established guild you'll probably find there's at least one crafter who can make you research items as you need them, either for free or they'll just need the materials
EU - EP - Dunmer - Dragonknight - Magicka DPS - CP160
There are various addons you can get from esoui.com that can help with that. I think one called research assistant might be useful but it's been a while since I used them. Most important traits to get researched are divines on all gear pieces, infused on head, chest, and legs, then all the other traits. Weapons you'll want to research precise and sharpened, Nirnhoned if you can afford it, then other traits.