I'm working here in saudi arabia for 19 yrs.If I'll exit for good,and the company give my end of service benefit,will I pay zakat the moment I receive the amount which above the nisab or I'll wait for a year to pass and pay the zakat?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

The Permanent Committee for Fatwa and Scientific Research issued a Fatwa that it is not an obligation to pay Zakat on end of service benefit except if it reaches the Nisaab (minimum amount liable for Zakah) by itself or with other Zakatable money added to it, and provided a whole lunar year elapses from the moment of receiving it. 

Allaah Knows best.