How can I give a url to the nintex form and nintex task associated with the workflow using send notification insert reference variables?
If you are asking about inserting a workflow task URL into notifications generated by the task, you would insert the "ApprovalURL" from the Common Reference section, using the Insert Link button on the toolbar. The item link, likewise can be inserted using the ItemURL from the Common References.
If you want to insert these links into just Send Notifications controls, you can use the ItemURL as suggested above. However, the link to a workflow task would need to be constructed from variables pulling in Workflow Task list url and the Task list item id (from the workflow) to construct the exact url.
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