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You cannot target the same thing 3 times with Jaya's Immolating Inferno but, yes, all three targets would receive +2 damage, thanks to Torbran, Thane of Red Fell. (and this is a replacement effect (rule 614), not a trigger (rule 603))
115.3. The same target can’t be chosen multiple times for any one instance of the word “target” on a spell or ability. (…)
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RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules