As per section 8(1)(j) of the RTI Act, 2005 the income tax returns, movable and immovable property, details of investment, salary, show causes or punishment issues of an employee, caste details etc are exempted from disclosure, unless a larger public interest is involved.
You have to show that there is some public interest involved in this information.
You can try filing RTI to get the EPF or Income tax returns of your wife. But in order to obtain the information, one has to show the public interest involved in asking the information, Meaning that how the information asked will be beneficial to the public at large.