Hi John L ,
Welcome to Microsoft Q&A platform and thanks for posting your question here. As I understand your question, you want to know what the required permissions are in order to create/use linked service in Synapse and for your case, the source is ServiceNow. Please let me know if that is not the ask here.
To use the Azure Synapse linked service associated with ServiceNow, you will need the Synapse User and Synapse Credential User roles on the Workspace System Identity. These roles will allow you to read and use secret credentials for the linked service.
Kindly checkout the following supported documentations :
Tasks and required roles to perform common tasks in Azure Synapse
Copy data from ServiceNow using Azure Data Factory or Synapse Analytics
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