can I pan sear previously smoked trout filets?
You can, but you shouldn't. Unless you want smoked trout sawdust or leather. Smoked fish is already fully cooked, and cooking it at such a high heat as to sear would pretty much finish it off moisture-wise. It really just wants gentle, moist heat if you wish to eat it warm. You can steam it lightly, or reheat it in a sauce or butter to help maintain some moisture. You could also make your sauce first, get that nice and hot, and then add the fish off the hob to warm gently in the residual heat. The only way I can think of that you might be able to sear or fry it would be as a fish cake or patty, which would be providing moisture from the mix.
Smoked trout is usually eaten chilled at maybe room temp, and not like you sit down to a plate with a fillet of smoked trout either- it’s a strong flavor. Usually it’s incorporated into another dish, like added to a salad, or a fish chowder, or perhaps on a bagel sandwich