Maintenence Case

you can demand all this document under section 91 CRPC after your evidence. if he do not present this document presumption will take against him.

ask him to provide detailed affidavit in Maintenence case

if u could get no details.. then nominal income Rs.1500/-pm will be assumed for which u need no proof

or else engage a detective agent..

Hypothetical question.. it depends on his nature of job. 1) if he files income tax try to receive his PAN or Naadhar 2) if govt servant. try under RTI Act. but not guarantee.. 3) property details..

Investigate about him to find his income