Why ask of past questions when it seems there wouldn't be test for experienced applicants. Also why ask of format of interviews? Are you not experienced? Rehearse the experience listings you noted in the CV you submitted, and be sure you can answer any questions issuing therefrom. Rehearse basic interview questions like what is short term and long term goals; challenges you have met while doing your work and how you solved them; etc. Read extensively about NNPC, its history, alliances & subsidiaries, Joint Ventures, operations, management structure/leaderships, etc. You don't really need any format if indeed you are experienced. But above all, God is the key.