If supplier suddenly told that there is raw materiel shortage how to deal or how to handle such situation?

I check my stock reserve and adjust quantity to order accordingly

All you need to do is to make a fast plan by contacting another supplier. That's why when working you don't have to stick to one supplier because anything can happen so there's need for more supplier.

you make a requisition so that services are available as soon as possible

This situation can be deal with keeping reserve stock or the other way is to track the inventory with organisation departments.

A business should always have a back up plan to handle such situation, hence we should arrange the shortage from a back up supplier.

supplier can be compelled to outsource anywhere else

To Save the line we have all 1 day with its night so we can take up with supplier to solve quality issue and then only shipment will be deliver without any quality issue.

need to check invoice and verified discrepancy then coordinate buying team and inform them by mail.

Yes, These staff need to be trained so that quick action can be taken until the safety team arrive.

cotinue the work slowly reduce the amployers and make the raw material for own self

Quickly look for a new supplier, and therafter should not depend on one supplier and it will also help to negociate a better price with suppliers too.