Focus on Dwarf Soldiers. They drop bolts and crossbows which sell well, and the experience is steady. Avoid Dwarf Guards unless your skills are 75+ and you have plenty of health potions (UHs).
At this stage, you should have roughly 70/70 skills. You can now move away from "trash" mobs and start hunting for profit. Tibia 7.4 Knight Leveling Guide
Explore the deeper levels for Rotworms and Orcs. Focus on Dwarf Soldiers
This is where the true Knight experience begins. You are now strong enough to hunt the bread and butter of the 7.4 Knight: Dwarf Guards. At this stage, you should have roughly 70/70 skills
If playing on a customized 7.4 server with Tiquanda or Ankrahmun, these areas offer massive mob density. Survival Essentials
At this level, you transition from a solo grinder to a vital team member.