[RPG] Does Two-Weapon fighting work if you aren’t holding both weapons when you take the Attack action

You need to be holding both weapons when you Attack in order to use Two-Weapon Fighting.

So no, you cannot RAW get the bonus from Dueling on both attacks, but you could still get it on one of them.

Let's work this through...

1. Yes, you can throw a dagger with your Attack action, and then make a bonus-action attack with your offhand weapon

Mechanically, this works fine. You start your turn wielding two light weapons and throw the first with your attack action. Two-Weapon Fighting (TWF) rules state:

If either weapon has the thrown property, you can throw the weapon, instead of making a melee attack with it.

Then you can use your bonus action to attack with the second weapon as per the TWF rules. So far so good.

2. And yes, it is possible to get a bonus from Dueling on thrown attacks

The text from the Dueling fighting style (p. 24 SRD) says:

When you are wielding a melee weapon in one hand and no other weapons, you gain a +2 bonus to damage rolls with that weapon.

While a plain-text reading seems to suggest that the Dueling bonus requires you to be wielding the weapon when damage is rolled, this interpretation has been specifically overruled by rules designer Jeremy Crawford in an unofficial tweet from October 2015:

Q: Does the Dueling Style apply its bonus to a thrown melee weapon?

A: Yes.

You are, of course, welcome to rule either way at your own table. Related question: Does Dueling Fighting Style apply to thrown weapons?

3. But you can't draw and attack with your second weapon, as a bonus action, after throwing your first weapon

This used to be the most contentious part of this answer, but has been explicitly confirmed by the 2020 edition of the Sage Advice Compendium:

Can I make an attack with one weapon, then draw a second weapon with my other hand and qualify to use two-weapon fighting?
To use the two-weapon fighting bonus action (PH, 195), you must have both weapons in hand when you make the first attack.

For my original reasoning, which brought me to this same conclusion independently, see the spoiler text below.

The relevant part of the rules for Two-Weapon Fighting states:

When you take the Attack action and attack with a light melee weapon that you’re holding in one hand, you can use a bonus action to attack with a different light melee weapon that you’re holding in the other hand.

While it's not completely explicit, this is generally understood to mean that you must already be holding both weapons, when you take the Attack action with the first weapon, in order to have the option of making the bonus-action attack with the second weapon.

This reading is supported by the fact that it's often stated that D&D 5e 'only does what it says it does' (see the answers to this question: What is the source of the "spells do only what they say they do" rules interpretation principle?). The text here emphasises that both weapons are being held (bolded above); if holding both weapons was not an important part of this ruling, then it could instead have been rendered like this:

After you've taken the Attack action and attacked with a light melee weapon with one hand, you can use a bonus action to attack with a different light melee weapon, using your other hand.

Writing the TWF rule like this would have removed any suggestion that both weapons must be held at once, and it would also be more succinct. The fact that they didn't express it like this suggests that those extra words are an important part of the TWF rule, and add something specific to the criteria a PC needs to meet in order to use Two-Weapon Fighting.

For evidence of consensus on this ruling elsewhere, see these other related questions:

- Can you benefit from the Dueling fighting style for one weapon, then draw a second weapon as part of Extra Attack to qualify for Two-Weapon Fighting?
- Can I draw a weapon before making a bonus-action attack and get the damage bonus from the Dueling fighting style?

So, it's possible to use your free object interaction to draw your second weapon, after having thrown your first weapon (getting a Dueling bonus on that first attack). But, you wouldn't then be able to attack with your second weapon on the same turn, as you wouldn't have met the criteria needed to trigger the option of a bonus-action attack from TWF (i.e. holding both weapons at the time of your first attack).

4. However, you could still get the Dueling damage bonus on your second attack

If you were holding both weapons when you made your first attack, then you meet the requirements for Two-Weapon Fighting. Having thrown your first weapon as part of that attack, you now meet all of the requirements to get the Dueling fighting style's bonus on your bonus-action attack:

When you are wielding a melee weapon in one hand and no other weapons, you gain a +2 bonus to damage rolls with that weapon.

And, as shown in part 2, you can get that bonus Dueling damage regardless of whether you make a melee or a thrown attack with that weapon.