[RPG] Does a spell attack trigger extra damage from Hexblade’s Curse

Add your spell attack bonus to each attack roll.

When a spell tells you to make an attack roll, that means you roll a d20 and add some bonus to get the final value. If that final value matches or exceeds the target's AC (Armor Class), then the attack was successful, otherwise it was not. Chapter 10 of the Player's Handbook defines this term in the subsection "Attack Rolls", and says the following:

Some spells require the caster to make an attack roll to determine whether the spell effect hits the intended target. Your attack bonus with a spell attack equals your spellcasting ability modifier + your proficiency bonus.

And the text of Scorching Ray (Chapter 11) says that the caster should make an individual ranged spell attack roll for each ray:

You create three rays of fire and hurl them at targets within range. You can hurl them at one target or several.

Make a ranged spell attack for each ray. On a hit, the target takes 2d6 fire damage.

For each ray, you roll a d20 and add the spell attack bonus to the roll, and determine whether that ray hit your intended target. If a ray hits, then roll to calculate the damage from that ray. Attack rolls and damage rolls are independent from each other, and in the case of Scorching Ray, each ray's damage is 2d6 (i.e. sum of 1d6+1d6).

Ultimately yes, with some caveats that I think may not be what you are intending.

The Eldritch Smite warlock invocation (XGtE, p. 56) reads:

Once per turn when you hit a creature with your pact weapon, you can expend a warlock spell slot to deal an extra 1d8 force damage to the target, plus another 1d8 per level of the spell slot, and you can knock the target prone if it is Huge or smaller.

This is an extra die or dice that is/are added to your damage roll, the same with Hex:

Until the spell ends, you deal an extra 1d6 necrotic damage... PHB pg. 251

"Damage rolls" are specified on pg. 196 of the PHB:

Each weapon, spell, and harmful monster ability specifies the damage it deals. You roll the damage die or dice, add any modifiers, and apply the damage to your target.

Since each ability specifically states that your "damage roll" and not "damage die/dice" are getting the boost, this indicates the following:

It does not add an extra +2 to each die that is rolled, just to the overall result of all dice rolled for damage. This also applies to Hexblade's Curse:

You gain a bonus to damage rolls against the cursed target. The bonus equals your proficiency bonus. -XGtE pg. 55

They can stack though, with both being applied at the end of all damage rolled.

Dueling in the PHB on pg. 72 reads as such (emphasis mine):

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.

Also of note is that if you are wielding the Polearm two-handed, it does not add the extra damage, as it is explicitly stated it must be in one hand.

It should also be kept in mind that the Eldritch Smite invocation is boosting the damage of an attack you are already making, so it is not Eldritch Smite that is getting an additional damage die by Hex but the damage roll while using Eldritch Smite.

The end result of all of the above being used at once, assuming you are using a Quarterstaff as your pact weapon since that is one of only two polearms (the other being a spear with the same damage die and different damage type) that can be used one handed, would be on a hit your damage roll consists of the following: 1d6 bludgeoning (Quarterstaff), 1d6 necrotic (Hex), 2d8 force (Eldritch Smite [assuming level 1 slot]), +2 (dueling style), +2 (Hexblade's Curse adding proficiency bonus assuming low level in both classes), +3 (an assumed value for your Strength modifier)