Alert log file location in oracle

Please check diagnostic_dest paramter in oracle to find out diag destination and alert log will be inside that only.

select * from v$parameter where name like '%diagnostic_dest%';


ex:

ORACLE 12102@<servername>#/usr/local/oracle/admin/diag/rdbms/sample91/sample91/trace

ORACLE 12102@in1fdsrst01#ls alert*
alert_sample91.log
ORACLE 12102@in1fdsrst01#tail alert_sample91.log