UIkit needs jQuery but it’s called from Stacks, not from the theme template or any of the UIkit stacks. Note that you can always use the resources to call a specific version of jQuery, this is not something I would recommend but here it goes…example (this goes in the custom header):
<script src="%resource(jquery.min.js)%"></script>
This is not necessary. You can enable jQuery locally in Stacks by disabling this option in the Stacks preferences:
If you’re unfamiliar as to where the Stacks Preferences is found you can click on this icon here to open the Stacks Preferences pane:
