Warlocks and Spellbooks

There is nothing in the 2024(5.5) PHB that covers this so:

1. Can a Warlock learn spells from a Wizard's spellbook?

2. What if the spells are on the Warlock's spell list? Does that change things?

3. What if the Warlock has the Pact of the Tome feature: Does that change anything?

Thanks.

No.  From 2024 phb for warlock:

"The number of spells on your list increases as you gain Warlock levels, as shown in the Prepared Spells column of the Warlock Features table. Whenever that number increases, choose additional Warlock spells until the number of spells on your list matches the number in the table."

"Changing Your Prepared Spells. Whenever you gain a Warlock level, you can replace one spell on your list with another Warlock spell of an eligible level."

That is the only mechanism for a warlock to gain spells or change spells.

I think wizard is the only class that has access to unlimited spells via their spell book. But even then, they can only prepare a fixed number based on their level

Quote from zanzibozo >>

There is nothing in the 2024(5.5) PHB that covers this so:

The rules very much do cover this, because the ability to learn spells from a spellbook is part of a class feature that's specifically granted to the Wizard class. If you don't have that class, you don't have that class feature, and therefore that's not a thing you can do. 

In general, the rules for D&D classes list the things they can do, not the things they can't do, so you won't find any rule that explicitly says Warlocks can't learn spells from a spellbook. But the Pact Magic class feature defines the ways in which you can learn new spells, and copying them from a Wizard's spellbook isn't one of them, so that's not a thing you can do.

Pact of the Tome gives you another way to learn new spells, but it makes no mention of copying spells from a Wizard's spellbook, so it doesn't change anything in that regard.

Quote from zanzibozo >>

[...] 2. What if the spells are on the Warlock's spell list? Does that change things? [...]

 I'm not totally sure if this is interesting for you, but the next SAC is relevant to determine whether game features interact with class spells:

Which of a character’s spells count as class spells? For example, if I’m playing a Sorcerer, which of my character’s spells are Sorcerer spells?

A class’s spell list specifies the spells that belong to the class. For example, a Sorcerer spell is a spell on the Sorcerer spell list, and if a Sorcerer knows spells that aren’t on that list, those spells aren’t Sorcerer spells unless a feature says otherwise.

EDIT: (short!) threads with examples related to this ruling:

• Magic initiate and class spell list
• Cultist initiate question?
• Agonizing Blast can apply to which cantrips?

Warlocks automatically and freely learn spells when they level up.  They get no benefit from having a Wizard's Spell book with or without the spell in it.

Quote from wagnarokkr >>

Pact of the Tome gives you another way to learn new spells, but it makes no mention of copying spells from a Wizard's spellbook, so it doesn't change anything in that regard.

This isn't quite right. Pact of the Tome gives you access to additional spells, but it should be noted that you pick those spells each time you summon the tome and never actually learn them. You can only use the spells while the tome is on your person.