The URL for the task is something like  http://{FormsServer}/forms/form/approval/{Resume_Id}, the resume id is dynamic generated for each task and you can find it from the cf_bp_instance_approvers table.  But there is currently no easy way to get the link of a user task from an email service task. 

Can you change the task email notification to all use external links?  By default, the Forms server URL in user task use the Primary Forms Server URL configuration. But in Forms 10.2.1, there is an option called "FormsHostEmailOverride" added to control the link in user task notification, the format of it is http://v-sh-win7x64-24/forms/ which is similar as Primary Forms Server but different from FormsURI(http://v-sh-win7x64-24). You can this option in cf_options table to customize it.