After installing the latest version of K2 (v2.8) with PHP 7 I get an error message in the user module:
Non-static method JApplicationSite::getMenu() should not be called statically in /home/users/mysite/modules/mod_k2_user/helper.php on line 94
Deprecated: Non-static method JApplicationCms::getMenu() should not be called statically in /home/users/mysite/libraries/cms/application/site.php on line 272
Line 94 in the helper.php file reads:
$menu = JSite::getMenu();
This should be changed to:
$menu = JFactory::getApplication()->getMenu();