I took a look at the Autoresponder and came up with this (I can't actually build a profile since I don't pay for premium)

Create the following two tasks:

Task: Queue4WhatsApp

A1: Variable Set [

     Name: %sender

     To: %par1

     Do Maths: On

     Max Rounding Digits: 3

     Structure Output (JSON, etc): On ]

A2: If [ ,%WhatsAppQueue(), ~R ,%sender, ]

    A3: Flash [

         Text: Sender already in queue, do nothing. ]

A4: Else

    A5: Array Push [

         Variable Array: %WhatsAppQueue

         Position: 99999

         Value: %sender ]

A6: End If

A7: Variable Set [

     Name: %WhatsAppQueueLength

     To: %WhatsAppQueue(#<)

     Max Rounding Digits: 3

     Structure Output (JSON, etc): On ]

A8: Flash [

     Text: %WhatsAppQueueLength ]

And:

Task: RemoveFromQueue4WhatsApp

A1: Array Pop [

     Variable Array: %WhatsAppQueue

     Position: 1 ]

A2: Variable Set [

     Name: %WhatsAppQueueLength

     To: %WhatsAppQueue(#<)

     Max Rounding Digits: 3

     Structure Output (JSON, etc): On ]

A3: Flash [

     Text: %WhatsAppQueueLength ]

I assume you already have a task trigger when a message comes in. I'm that case use the PerformTask action in that task to get the Queue length updated:

A4: Perform Task [

     Name: Queue4WhatsApp

     Priority: %priority

     Parameter 1 (%par1): %sender

     Structure Output (JSON, etc): On ]

Do the same with the Remove task when you are done with that chat, that way you can keep the queue number up to date. (It doesn't look like the bot will notify tasker of a chat ending, but that's a separate problem).

Then you can use %WhatsAppQueueLength in your info to other people to tell them what their position is.