Sometimes, instead of saying "could/can" or "would/will" (the two most common I've heard), some people say "could/can do" or "would/will do".
I don't know if it can.
I sometimes (but uncommonly) hear:
I don't know if it can do.
Say them with a mild emphasis on the italicized can and you'll be saying it as I hear it.
As this is a little hard to express to someone who has never come across it before, I hope someone who sees this knows what I mean. Why is that extra "do" sometimes used?
Additional note: Here are three examples that in jwpat7's opinion may be similar to or represent what Daniel δ refers to:
I have never crossed the Himalayas, though I might have done. - Christopher Hughes, 2006
...when I could get a vote for Mr. Charlesworth, I did do. ... I made no regular canvass, [but] where I could get a vote, I did do. - Slade testimony, 13487-8, 1860
"... When needed I will turn myself in too. And if I can do, you can do too!" - Oblivion in Progress, 2011, pp. 67-68