Please ignore it. It seems that I was just too fast to ask the question or too slow finding the answer myself.
P.S. The answer is to go to expensions/SemanticMediaWiki//includes/SMW_Settings.php and edit $smwgNamespacesWithSemanticLinks array.
I seem to have a problem using Semantic MediaWiki with non-default namespaces. There is no Infobox and data is not searchable using Special:Ask
Is this a limitation of current version or just some mistake in configuration?