To address the visualization within WDQS (and not the dereferencing): Would a new prefix wdunkownvalue: <http://www.wikidata.org/.well-known/genid/> added to wikibase.queryService.RdfNamespaces.NAMESPACE_SHORTCUTS.Wikidata be a feasible solution? It doesn't sound too complex, and the descriptiveness of the prefix might guide WDQS users to the correct conclusion regarding its meaning, even those not familiar with skolemization and well-known URI as skolem IRIs.

@Lea_Lacroix_WMDE I found some in p:P547/pq:P1932 when I created https://www.wikidata.org/wiki/User:CamelCaseNick/Stolpersteine/Hamburg/Mitte, e.g. http://www.wikidata.org/entity/Q66148105 contains U+0308 in Müller (https://w.wiki/pZZ).

This problem also effects umlaut characters vs the use of the diacritics Unicode character U+0308. (And ListeriaBot cannot save the latter.)

The issue doesn't seem to be solved. For example