How can I check if user has an authorization for T-Code or not in SAP system?

To check if a user has authorization for T-code or not you can use Transaction SUIM. You can manage user permissions using different ways like profile assignment via a single role, collective roles that contain single roles, etc.

 Below shows SUIM transaction that opens User Information System as below:

You can also join tables: AGR_USERS and AGR_1251

AGR_USERS is a standard SAP Table which is used to store Assignment of roles to user information. This is available within R/3 SAP systems depending on the version and release level.

AGR_1251 is a standard SAP Table which is used to store Authorization data for the activity group information. This is available within R/3 SAP systems depending on the version and release level.