Dynamics 365 - Count Waiting Worklow Sessions

Use the below query in FetchXML Counter plugin in XrmToolbox to count the workflow sessions in waiting state.

<fetch version="1.0" output-format="xml-platform" mapping="logical" distinct="false">
  <entity name="asyncoperation">
    <attribute name="asyncoperationid"/>
    <attribute name="name"/>
    <attribute name="createdon"/>
    <attribute name="statuscode"/>
    <attribute name="statecode"/>
    <order attribute="createdon" descending="true"/>
    <filter type="and">
      <condition attribute="operationtype" operator="eq" value="10"/> <!-- 10 corresponds to workflow -->
      <condition attribute="statecode" operator="eq" value="3"/> <!-- 3 corresponds to waiting state -->
      <condition attribute="name" operator="like" value="Modified date Ageing reminder"/> <!-- Replace with the name of your workflow -->
    </filter>
  </entity>
</fetch>