I'm coming up the the demonknight in durlags tower. I remember being able to cheese this fight in the past but that was with a full party. this time around I have just a sorcerer and Alora. It's not all bad news though, I removed the lvl cap so the sorcerer is about lvl 11 and alora lvl 10. Is the demonknight doable?

Ring of fire protection. Protection from magic scroll/potion. Mirror image/Blur. Smash the mirror. Depending on what weapon you use, weal on him or kite him. Magic protection and not getting hit is key.

Since you are playing a sorcerer I suppose you are playing either BGT or EE. If he has the same stats as in vanilla, and you want to defeat him without using mirror, you need some heavy physical damage dealt to him, since he has magic resistance. Depending on your sorcerers stats and spells, you can either use tenser's transformation or use summons to tank him. You must prepare to face the following spells: dispel magic, fireball and stun.

Ring of fire protection is great. You can get one in the area east of Nashkel mines (the place where a woman asks you to return an injured man to the Friendly Arm Inn), and/or by following the main story (you won't get it until way later). It stacks with any other fire protection you have already. I killed him with one melee. I had Imoen, Garrick, and Ajantis assault him with bolt/arrows of biting. I had Xan hit him with Melf's acid arrow, and Larlock's minor drain. sometimes I would have Garrick throw some magic missiles at the knight too. The tick from these attacks (not sure if magic missile counts as a tick) will hopefully disrupt his spellcasting.

I equipped my melee with the +2 large shield (you get this at Durlag's tower), full plate (if you are at this point, you probably found something comparable) , gauntlets of weapon expertise, a +2 longsword (aka Varscona), Kiel's helm (which you also get in Durlag's tower), ring of fire protection, and boots of speed. The potions I used were: potion of frost giant strength, oil of speed, and potion of magic blocking. When you engage the Demon Knight, he will dispel magic first, so use the potions *after* this happens, and remember to take the potion of magic blocking last, because there's a chance it could block the effects of the other potions. The dispel magic is followed up with a fireball. This fireball is the game's equivalent of an ICBM; and can easily lead to a TPK.

I wouldn't recommend smashing the mirror, because the summoned monsters will fight you too. If the monsters kill him instead of your party, you won't get any XP for the knight.

Edit: I recommend using a potion of agility. If your dexterity is already 18+, a potion of mind focusing would come in handy.

if you have Polymorph Self, kiting from flind of spider form might work. WIth summons and buffs, of course.

For kiting, by that time you should have the boots of speed