When I use scorching ray, would I add my spell attack bonus to each ray? Like I cast the spell, hit my target all 3 times I roll 2d6+spell damage three times, or 2d6 three times then add spell attack?
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).