@Avinash.Haridasu 

https://hostname:port/prweb/api/v1 /nodes/{nodeID}/queue_processors

Get all queue processors on all nodes. This API is supported only on 'all' nodes (In nodeID path parameter individual node ID is not supported).

so, https://hostname:port/prweb/api/v1/nodes/all/queue_processors would return information about all the QP's running.

Response contains numOfScheduledMessages which you might be interested in. 

{
  "status": "200",
  "servedBy": "2101da3bec88",
  "data": [
    {
      "readyToProcess": "0",
      "nodeType": "BackgroundProcessing",
      "numOfBrokenMessages": 0,
      "numOfScheduledMessages": 0,
      "queueClass": "-",
      "name": "pzStandardProcessor",
      "state": "Running",
      "processedInLastHour": 0
    },
    {
      "readyToProcess": "0",
      "nodeType": "Search",
      "numOfBrokenMessages": 0,
      "numOfScheduledMessages": 0,
      "queueClass": "System-Queue-BIIncrementalIndexer",
      "name": "pyBIIncrementalIndexer",
      "state": "Running",
      "processedInLastHour": 0
    },
.......
}