wizard spell slots by level
Fighter - bg3.wiki
The Spell must be one for which the Wizard has a spell slot, even if they obtained it by multiclassing (so a L4 Cleric / L1 Wizard can transcribe Level 3 spells).
Druid | D&D 5th Edition on Roll20 Compendium
If a wizard copies itself, the simulacrum has the spell slots the wizard has, though the copy can never regain spell slots.
Ranger 2024 » Dungeons & Dragons - D&D 5e - aidedd.org
For example, a Wizard will gain 2 level 1 Spell Slots at level 1. However, for a class like the Paladin, they'll need to reach level 2 first to obtain their first 2 spell slot casts.