Query Custom Object Data - Application Composer

Summary:

How do we query data in a custom object from another custom/standard object? 

Content (required):

Hi,

In Application composer, How do we query data in a custom object from another custom/standard object? 

I have a custom object where some data is saved. I want to access this data from standard object(change order). 

I understand the custom object can be called as a webservice and can be queried.

Other than this, Is there a way to query custom object data from Application composer/groovy? Please let me know or share relevant documentation. 

Regards,

Sravanthi

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