Kitty: I'm waiting for a banana.
Jair: I, too, am waiting for a banana. (1)
Jair: I, also, am waiting for a banana. (2)
Which is correct, (1) or (2)? If both, what's the difference? Plus, are commas before and after too/also strictly required?
Both of these are correct in formal English, but they don't reflect actual speech.
Also is comparatively rare in speech, and almost never to specify that the subject is 'duplicated'. As Mistu4u tells you, it is usually placed immediately before a single lexical verb or immediately after the first auxiliary, regardless of whether it is the verb or the complement that it duplicates:
I have a banana, and I'm also waiting for a banana.
I have a banana, and I also have an orange.
I have a banana, and I've also been promised an orange.
Too is far more frequent, and it's almost always set at the end of the clause, regardless of which constituent is duplicated:
You have a banana, and I have a banana, too.
I have a banana, and I'm waiting for a banana, too.
I have a banana, and I have an orange, too.
By orthographic convention too is set off with commas wherever it falls; also is not set off unless it falls in an unusual place.