Hi,
First note that a workbook is not child resource of Log Analytics workspace. Workbook is standalone resource. You can assign Workbook Contributor on the workbook or on the resource group where the workbook is located in. Note that in order for the end user to see the data in the workbook it needs permissions corresponding to the data the workbook is accessing in. So if the workbook has queries towards Log Analytics workspace the end user will need Monitoring reader on that workspace.
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