assuming you are using soil, cover the exposed roots with earthworm castings and water in. will give the soil a shot of fresh goodness and the plants will respond happily.
Soil is correct, will do , for some that will work , as for 2 of them I believe they are a bit more filled up to the brim of the pots wish I had a picture on hand of the bases of the plants
I wouldn't worry about surface roots. If I uncover my mulch I see surface roots over every square inch of soil in only a few weeks of veg with 4 plants - in a 150 gallon pot! Those surface feeder roots are really common with organic methods, especially if you're top dressing and keep the upper soil horizon moist. It's where the most goodness is. And cannabis roots can grow faster than the upper part, especially in early growth stages.