I am using the double-bladed scimitar with the Revenant Blade feat from Wayfinder's Guide to Eberron.
The double-bladed scimitar's special feature (p. 74):
Special. When you take the attack action and make a two-handed attack with a double-bladed scimitar, you can use a bonus action to make a melee attack with the blade at the opposite end of the weapon. This attack uses the same ability modifier as the primary attack. The weapon’s damage die for this attack is a d4, and it deals slashing damage.
The part of the Revenant Blade feat (also on p. 74) that mentions the damage:
On your turn, when you use a bonus action to make a melee attack with the blade at the opposite end of the weapon, the weapon’s damage die for this attack increases to 2d4, instead of 1d4.
Let's say I have 16 Dex, so a +3 to my dex mod. If I take the Attack action with the weapon, and use my bonus action for the weapon's special function, do I add my Dex modifier to the damage of the special attack or not? Will it be 2d4+3, or just 2d4?