In the Advokat theme, when I try to add a secondary menu at any other location than "menu" module position, I cannot have the submenus show when I hover over the menu (like in the main menu in the "menu" module position). When I select "Show Sub-menu Items" = Yes in the module configurator, the whole menu structure is displayed statically (not what we want). What do I have to change to get the result desired?

Hello,
a dropdown menu is only possible in the menu position.
Accordion menu is possible only in sidebars and on all other module position there is only a basic menu without dropdown function.

Anyway you can add a custom html module with html code instead of a menu module on the position.
Therefore use the following code
getuikit.com/v2/docs/subnav.html

<ul class="uk-subnav">
<li><a href="">...</a></li>

<!-- This is the container enabling the JavaScript -->
<li data-uk-dropdown="{mode:'click'}">

<!-- This is the nav item toggling the dropdown -->
<a href="">...</a>

<!-- This is the dropdown -->
<div class="uk-dropdown uk-dropdown-small">
<ul class="uk-nav uk-nav-dropdown">
<li><a href="">...</a></li>
</ul>
</div>
</li>
</ul>

Problem solved.

Hello, Solved with a Custom module and the html instructions you sent, than you.