I know I can sort by “upgradeable”, but this only tells me that at least tier one can be forged.
However, this is barely useful to me, because I usually only forge traits to increase a kingdom level or to satisfy dailies.
In either case I’m only interested in troops that can get level (or tier) 2 or 3 traits. But currently the only way to know is to click through them.
I’m afraid my mouse won’t keep up with all that clicking…
Is there an easier way?
I believe if you make an account on gowdb.com, on My Collection, you should be able to sort by number of traits for your troops.
I’m not sure it can do what I seek - tell me which traits I can forge - but it’s a useful tool nonetheless, so it’s worth taking a closer look 
Since it knows how many traitstones I have, it shouldn’t be impossible to add that function, even if it’s not there currently.
In any case, useful information - thank you!
You seem to be changing the question from what troops are at traits 1, 2 or 3 to which traits on a troop can be forged.
The former is answered in My Collection - it tells you how many traits a troop has and the overall number of traitstones needed for the rest of the traits (and souls needed to level if at mythic and number of cards needed to level to mythic).
If you need to know which traits a troop has, you just click on the troop name.