I did not realize this feature was not in the Android app. I only found out there was no check number after I exported as a qif then imported into GnuCash for desktop.

I was hoping to use GnuCash for Android to record transactions while writing checks at my kitchen table, then importing them into GnuCash for desktop. Unfortunately, since GnuCash for Android does not record the check number I would have to manually record this information for each check transaction (I would also have to manually enter in the notes I record for each transaction even though the app allows you to input notes, but does not export them in the qif file; but that's another topic) If I have to manually record the check number for each transaction I might as well just go to my office and record the whole transaction at my desktop computer instead of going through the extra steps required to use the Android app.