Retrieve Metadata values from ROQL

Summary

Query to get incident custom menu field items

Content

Hi All,

I want to display a custom menu field values into a multi select drop down field.So I would like to retrieve a custom menu field value under the incident object. The difficulty I am facing is I am not able to get the values of menu field unless it is not stored against the incident object.

Please refer the attached image of the menu field,from that I can't get the highlighted values.

"Select customFields.c.x_trial_type.LookupName FROM Incident WHERE customFields.c.x_trial_type IS NOT NULL GROUP BY customFields.c.x_trial_type.LookupName"