Via Infotype
TRY.
DATA(lo_employee_api) = cl_hcmfab_employee_api=>get_instance( ).
DATA(lv_pernr) = lo_employee_api->get_employeenumber_from_user( sy-uname ).
DATA(lv_ename) = lo_employee_api->get_name( lv_pernr ).
CATCH cx_hcmfab_common.
ENDTRY.
or via SU01
DATA(lv_ename) = NEW cl_hreic_appl_utilities( )->get_user_name( sy-uname ).