This feature is now available for the server & data center versions.
As a Jira administrator navigate to the Issues → custom fields screen where all the custom fields are listed. Click on 'add custom field' action.
In the pop-up that opens, select 'all' custom fields & then search for 'objective'. Click on 'next'.
In the next step, add a name for the custom field along with appropriate description. Do note that there is no restriction on this field name or description, they could be anything that might suit your needs. Click on create.
On creation, the field will be displayed in the list of custom fields. Click on 'configure' (top right corner).
On the configurations screen, click on 'edit configuration' link just after 'applicable contexts for scheme'.
Depending on how you intend to use this custom field, you can select relevant context/issue types. If you are not sure, keep it unchanged (Global).
Back to the configurations screen, don't worry about the 'default value' configuration. Click on 'edit attribute name'.
This screen will allow you to choose any one of the available Employee Success objective attributes. You can even create multiple custom fields & then assign different attributes from Employee Success objectives.
For example, let us set it to 'objective title' attribute. Now go back to the custom fields listing page & click on 'screens' option from the top right corner (for the custom field you just created).
Here you get to select, on what screens this custom attribute will be available. Check the ones that are suitable for your needs.
Post this, run the indexing job from administration → system → advanced → settings
Now navigate to any of the issues that are eligible to have this custom field & notice the field appearing with relevant Employee Success objective title populated. This field will appear empty, if the issue is not connected with any Employee Success objective as key result.
Since the indexing job was run already, one can use this custom field in JQL as well. If necessary, you can also add this custom field as a column in your 'issue search' screen.