Multiclassed casters learn/prepare spells as if single-classed in each class. The multiclass spellcasting rules in the PHB (p. 164) or basic rules clearly address how known and prepared spells work if multiclassed into 2 or more classes (or subclasses) with the Spellcasting feature:
How does multiclass spellcasting work in dungeons and Dragons?
According to page 164, when you are determining which spells you can learn or preparing a list of spells, you treat each class separately, completely ignoring the multiclass spellcasting section entirely.
Do you get to use your wisdom as a spellcaster?
You do not get to cast your wizard spells using your Wisdom as the spellcasting ability. Say that you are a 4th-level druid who gains a level in cleric. According to the Multiclass Spellcaster: Spell Slots per Spell Level table on page 165 of the Player’s Handbook, you have access to 3rd-level spell slots.
What are the rules for multiclass spellcasting in PHB?
The multiclass spellcasting rules in the PHB (p. 164) or basic rules clearly address how known and prepared spells work if multiclassed into 2 or more classes (or subclasses) with the Spellcasting feature:
What happens when you have more than one spellcasting class?
Your capacity for spellcasting depends partly on your combined levels in all your spellcasting classes and partly on your individual levels in those classes. Once you have the Spellcasting feature from more than one class, use the rules below.
How many spells do you need to multiclass?
You currently need to invest in 3 different spellcasting abilities on top of Dexterity for AC and Constitution for concentration saves. You’re also missing out on higher level spells like Dispel Magic, Fireball and Revivify that lower level spells simply can’t imitate even with higher level slots.
