Where and when can I find Kasumi Goto in ME3? Also is she only in ME3 if you recruited her and paid for the ME2 DLC?
Kasumi is part of the Hanar diplomat mission on the Citadel. She needs to have survived in the 2nd game.
You also must complete the mission in 3 before the story mission involving the Citadel, or else the mission is lost.
I think you have to have recruited her in ME2 to see her in ME3. Therefore, you would have needed to buy the DLC.
Kasumi is still around iN ME3 if she survived ME2 (meaning you got the DLC and she survived in your save). ME Wiki says she'll be on the Citadel, and she has some different dialog and scenes depending on whether you got her loyalty in ME2. She can be a war asset if and only if you won her loyalty.