How do I obtain Certification of my disability pension?
I'm not exactly sure what you mean by, "Certification of my disability pension"? I'll guess that you need a copy of any awards you have from VA and those are available on your eBenefits account.
Try starting your search for what you need here https://www.va.gov/disability/view-disability-rating/ Be patient, the VA system is a bit clunky some days. Good luck!