Hello,
1)Whether or not your job in the bank will be in danger depends on the stand the bank is going to take as a disciplinary action. It will also depend on the number of days you may require away from work for the exam.
2) It is not clear from your query if you have already gone for the exam without permission or you want to know what the consequences would be if you go without permission. If you have already remained absent you are liable to give an explanation for the absence. If you have not gone so far you could seek permission to attend exam and offer to go on leave without pay.
3) If you took off without leave being sanctioned or permission sought you can be suspended from job, salary deducted and increment may be affected as well.