When I check box is selected how to I add additional check boxes?

You can use the Show/Hide Field condition so that the other check box will appear based on the selected option from the first check box field.

Here's a demo form: https://form.jotform.com/62875699134976. You can clone it if you like. Here's a guide on how I created the demo form:

1. I created 3 check box fields.

2. Click the "Conditions" button in the toolbar.

 

3. Select the "Show/Hide Field" condition.

 

4. Create a condition wherein if the "Option 1" is selected in the "Check box 1" field, the "Check box 2" field will appear.

5. Now you can add multiple conditions depending on your preference.

Here's the result:

Related user guide: How-to-Show-or-Hide-Fields-Base-on-User-s-Answer

Hope that helps. Thank you.

Thanks. Is it possible to appear directly under the checked box instead of under all of the boxes?

...

If my understanding is correct, you want the added checkbox to be appended in between the Checkboxes group dynamically.

I.E.

when I select a checkbox on Checkbox 1 group, the new checkbox will be inserted in between those existing checkboxes. 

Unfortunately that is not how the workaround condition logic work. The condition will only add the new checkbox field separately. Actually it was not adding the checkbox field.. it was just making it  visible from the original hidden state. So it gives the illusion of it being added...

Perhaps an alternative widget you may want to check is the dynamic User contributed Checkbox widget.

link: https://widgets.jotform.com/widget/user_contributed_checkbox

It work differently as it requires input from user instead for the Checkbox option to appear. But you can see how it dynamically add the option on the Checkboxes.

You can test the demo form here https://form.jotformpro.com/form/43441792653964

Hope this help. Let us know if you need further assistance.