Since you are going to give interview, for inspector inland revenue, so you should have some knowledge of the three inland tax laws being administered by Inland Revenue
Income Tax Ordinance, 2001
Sales Tax Act 1990
Federal Excise act, 2005

direct tax, indirect tax, withholding tax, advance tax, tax avoidance and tax evasion, different types of income, and things like these may be important. and final picture would be clear once someone appears in the interview