An interesting theme, why not read it? Avoid: Ultimate Scheming System Reverend Insanity Death Scripture (not really, but just preventing it from being mentioned lmao).
Solo levelling - manga, MC known as weakest Dungeon Hunter in the country dies and wakes up with a levelling system.
I think there was a novel from the author of The Strongest System where the MC grows stronger after dying ... ... me thinks ... For stronger by killing ... Toika stories' MCs grow stronger, and most novel with an XP system should work like that
Suterareta Yuusha no Eiyuutan MC has blessing from dark/death goddess that make him become more powerful each time he die... however the novel is in hiatus or dropped... the LN also in same status
The Devil's Cage (Qidian novel, sorry.) Because of the game system's rules, he gets drops (depending on level) from people/monsters/spirits he kills. One funny moment was when the MC quickly rushed to fight a huge horde of enemies because he wanted the drops, but the "natives" in the world thought he was a really kind-hearted savior.
Not quiet sure...but by the thread title, are you looking for novel(s) where the MC's got stronger by actually dying? If so, there's a CHN novel "All Things Wrong" where it's MC got a buggy character playing VRMMO game: whenever he killed a monster, his EXP decreased; but if he got killed, he got tons of EXP But if you want novel(s) where it's MC literally got XP by killing, then maybe "Kumo Desu ga, Nani ka?" would fit the bill