Is there the gerund of the verb "can"?

First, I don't think you're actually looking for a gerund. In English, a gerund refers to using a verb as a noun, and since you don't have another conjugated verb in the last phrase, I think you're actually looking for a participle (and wikipedia tells me in Portuguese, gerúndio refers to an adverbial participle, so that makes sense)

Now, as DeepYellow correctly states, can, when used as a modal verb has no gerund/participle form (the word canning exists, but it refers to the verb can when used to mean putting things in cans for storage, etc.) If such a form is needed, we normally shift from using the modal can to the phrase to be able which has a participle form being able, so you could go with:

This technique is very powerful, being able to be extended to several other questions.

I believe this lies a little closer to your original sentence (assuming my poor Portuguese skills haven't failed me) in that it indicates that the fact that is powerful is somewhat derived from being able to be extended rather your original translation which indicates that it is independently powerful and also can be extended. However, this sounds a little disfluent, so I might prefer something like:

This technique is very powerful as it can be extended to several other questions

This technique is very powerful due to being extensible to several other questions.

You are correct, there is no gerund for can. Can, as used here, is an auxiliary verb, and English doesn't provide gerund forms for auxiliary verbs.

The translation that you received seems (surprisingly) good.