Hi @wanda_a,
You should find the indexer.log file in /opt/couchbase/var/lib/couchbase/logs/ in linux environment. By the way, you can check if the indexing service is enabled in your cluster, and if indexer process is also running.
Also, please check if index metadata was backed up during backup. For this you can check the gsi.json file located inside your backup folder.
Also, please check backup / restore logs located inside backup folder.
Thanks.