The fast way is to use Azure Resource Graph (ARG), go to the 'Azure Resource Graph Explorer' in the Azure portal:
resources
| where type =~ 'microsoft.operationalinsights/workspaces'
| extend customerID = trim(' ', tostring(properties.customerId))
| project id, customerID, name=tolower(name), type_='Log Analytics', subscriptionId
|join kind=leftouter
(
resources
// Just show Workspaces that have Sentinel enabled
| where type =~ "microsoft.operationsmanagement/solutions"
| where name has "SecurityInsights"
| parse name with * '(' s_workspace ')'*
| project name=tolower(s_workspace), type_='Microsoft Sentinel', subscriptionId
) on name
| project-away name1, subscriptionId1
| project-rename Workspace=type_, MicrosoftSentinel=type_1
| order by ['MicrosoftSentinel'] desc
You will then get a list - any Workspace that doesn't have the words "MicrosoftSentinel" wont have Sentinel enabled. Just remember Log Analytics is enabled for Sentinel as well. You can run parts of the query to get the lists separately if required.
Don't worry, when you run the KQL, you'll see the workspace name and Subscription information as well as the reduced data I've shown .