How can we use SAP in two PC same time by using same user ID?

There is a limitation of 6 user screens so you can use the same login for upto 6 screens in a same Computer or in a different computer without any issues. E.G if you have 2 users screens opened in one computer then you can open upto 4 in other systems. The SAP application server is well capable to differentiate if two different systems are using the same login ID for transactions. You can create reports about the usage of these two systems by providing the filter of "system id" to differentiate between the transactions done by these two systems using the same user IDThanks

Check your SAP system not restricting the multiple login. If not login using same id in two system by clicking continue with the logon ,without ending any other logon in system. But as per SAP Licence multiple logon to production system is not legal.