In an Azure Monitor/App Insights/Log Analytics Workspace workbook you can select one or more log (analytics/app insights) resources using the dropdowns once you start adding visualizations.
First, add a new workbook, then change the query:
From the Data Source dropdown choose “Logs”, then choose the Resource Type “Application Insights” or “Log Analytics”:
Also, you can use kusto to refer to other resources as I showed in my other answer to one of your questions: https://stackoverflow.com/a/64532549/932728
The link in the comments below gives more details about this and any limitations.
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