I want to show a level2 categories only in product details page in virtuemart,but there is no specific product details page
You can make an override in You template to include modules. Make up a unique position code and add code to include the wanted modules.
Otherwise noNumber has a module manager that covers most usage scenarios, free and paid version
https://www.regularlabs.com/extensions/advancedmodulemanager (https://www.regularlabs.com/extensions/advancedmodulemanager)
regards
Jörgen @ Kreativ Fotografi
e.g
$modules = JModuleHelper::getModules('myposition');
foreach ($modules as $module)
{
echo JModuleHelper::renderModule($module);
}