Please find an example attached to this article. In the zip file you will find an example process, screenshots, and a script to populate the variable used in the process step. (You can import the custom process and see the script directly in the process step too.)
The method is as follows:
You cannot get the requestor of the cancellation from the 'PWODecisisionHistory' with a simple $-notation. What you need is a script. But you cannot use a script in a mail template. Thus you must use a variable in the template which will be filled from outside (from the SendRichmail job).
In the attached example the mail template "IT Shop request - approval required" has been copied and the following modification made:
With the PC-notation you create a variable which has to be filled by the process step.
After that the process "VI_ESS_PWOHelperPWO send mail new task for approver" is copied and 2 parameters added in the job:
Value = "Requestor"
<the value is contained in the attachment>
The script populating the 'Requestor' parameter checks to see if this is an unsubscription. If it is it retrieves the requestor. If not it uses the "normal" value direct from the 'PersonWantsOrg'.