Hi I am trying to figure out if something would work for my character, he is a rogue 6/ Fighter 1 and I went with the dual wielding fighter type. if he were to wield two rapiers could he make a attack with both of them, and if the situation is right, be able to use his sneak attack bonus on both attacks, or would he only be able to use it on one of them?
Thanks for any help you can give me,
DBGreece
Unfortunately, rogues can only benefit from sneak attack once during their turn.
Incidentially, if you can somehow get an attack out of turn (like an opportunity attack, or a Riposte from a Fighter with the Battle Master Archtype [pg. 74]) then you can also add your sneak attack dice. But when it's 'your turn' you can only apply it once.
Edit: And yes, he could make an attack with both rapiers on his turn. Dual weilding is awesome, if you miss with the first attack, you can always try again with the second attack! 
Thank you so much! That is good to know that i only get it once per turn I will have to keep it in mind for my future building.
Again thanks,
-DBGreece
You're welcome.
Btw, you do mean the Dual Wielder feat, right? You can't use Two-Weapon Fighting with rapiers unless you took that feat (probably when you hit rogue level 4). Regardless of weight, they aren't "Light." The Fighting Style feature from Fighter doesn't do that for you.
Actually I did not know that you could only dual wield light weapons unless you took the feat. I was referring to the two weapon fighting style of the fighter, but basically I would just have to uses two short swords instead of rapiers then right? Or would that not work either and I would have to go with two daggers?
-DBGreece
Ooh, right! My bad. . . you can't dual weild rapiers without the 'Dual Wielder' feat. Sorry
I would go with scimitars! Because they kinda look like rapiers!!! :D Well ok, not really - but they look more like rapiers than short swords do.
I was just thinking about using rapiers because i just came into possession of a +1 rapier, but I have a +1 shortsword that will work just as well
Thanks for the further help,
DBGreece
Nice. 
Have fun! 
Shortswords have the Light property, so you're good there. The Fighting Style feature just lets you add your ability modifier to the Bonus Action attack when using Two-Weapon Fighting, when normally you can't.
Put another way:
A) Character must have a separate melee weapon in each hand.
B) Both weapons must have the Light property.
C) When they take the Attack action with one of those weapons, they open up the option to use a Bonus Action to make one attack with the other. The Bonus Action option provided by this rule is a standard attack roll with all normal modifiers.
D) But, you don't add the character's Strength or Dexterity to the damage.
If you have the Dual Wielder feat, ignore part B. You have to wield a separate melee weapon in each hand, but they don't have to be Light. A rapier is now valid for Two-Weapon Fighting. A greatsword is not, because it has the Two-Handed property and can't be wielded in just one hand.
If you have the Fighting Style class feature (which fighters do), and you take the Two-Weapon Fighting option, ignore part D. You add the appropriate ability modifier to damage. This means the Bonus Action attack is identical to all the other attacks you make with your Attack action, except for using a separate weapon. Since it's not part of the Attack action, however, you can't substitute it for a grapple check, etc. You also don't get it back when you use Action Surge.