Hi
My wife filed petition to adjust my status. Since her income is below the poverty guidelines she didn't meet the requirements and so we have to find a joint sponsor. We already filed the case without the joint sponsor document. We have a letter saying my biometrics is on 10th Feb. Please should we send the joint sponsors documents now or should we wait until they request for it?.

Wait till they request it

I may disagree,
If you know you need it, first you were lucky they even accepted it. And they may also deny your petition without it. And the requirements for the joint will need last three year income taxes with all W2 and schedules.

And a joint signer is not always easy to find because the forms require the signer to be liable for the alien if they would get any welfare