Some of the users(mostly non-admins) do not see the "Subscribe" button in knowledge portal for knowledge article.

The non-admin user does not see the "Subscribe" button in the knowledge portal(kb) and not able to subscribe to the knowledge articles.

Service portal

The system properties "glide.knowman.enable_km_subscription.roles" manages the users who can see the subscribe button in knowledge portal.

In OOB, the property 'glide.knowman.enable_km_subscription.roles' is set to the role 'knowledge'. Edit this property to show the subscribe button to other role users as well.

Refer the below docs for more details:

https://docs.servicenow.com/csh?topicname=configure-subscription-properties.html&version=latest