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.
