Using a Nintex Workflow you can send an email with a link to the list item or nintex form by using the Common > Item Url reference, the potential problem is the Item URL reference is the link to the list item in Display mode.
Using a Regular expression action in your workflow you can create a link to the list item so when it opens the list item or nintex form will open in Edit mode.
1. Open up the Nintex workflow (or create a new Nintex workflow), click on the dropdown arrow under Workflow Settings and select the Variables option:
2. Click the New option.
3. Enter a name for the new variable, leave the type as Single line of text, click Save to create your Variable.
4. Click Close to return to the Workflow screen.
5. Add a Regular expression action to workflow, above where the email action is or will be.
6. Double-click the Regular expression action to configure it, for Pattern type in DispForm.aspx, for Replacement text type in EditForm.aspx.
7. In the Input text field, click on the Insert Reference option. Choose the Item URL reference from the Common tab.
8. Select your workflow variable in the Store Results in dropdown field. Once your Regular expression action is all setup, click on the Save button.
9. Add an Email action after your Regular Expression action, double-click the email action to configure it.
10. In the text area of the email, click where you want your link inserted, then click the Insert Reference option. From the Workflow Variables tab, select your workflow variable.
You will now have an email with a link to the List Item or Nintex Form in Edit Mode instead of in Display Mode: