This is a recipe for whole smoked trout or kokanee. If you want to smoke fillets, I'd go to my smoked lake trout recipe, which is meant for bigger fish. I prefer alder, oak or maple wood to smoke over, but it's your call.
Mix the salt and sugar with a gallon of water and stir to dissolve the salt and sugar. Submerge the trout in this brine and put in the fridge, covered, for at least 2 hours and up to overnight.
Remove the trout from the brine (discard the brine), pat dry with paper towels and set on a rack over a baking sheet in the fridge for at least a few hours, and up to overnight. You can also set the fish to dry in a cool, breezy place for a few hours.
Put the fish in the smoker, hanging or on the grates, and get a nice cool smoke going. Slowly let the temperature rise to 200F and hold it between 175F and 200F for at least an hour, and up to 4 hours; I prefer 2 hours. Do not let the temperature get above 225F. If it does, set a tray of ice in the smoker.
When your trout are smoked, you can eat them warm or chilled.