Question: What royal or noble rank does the head of state of the Kingdom of Mercia hold?
Paraphrase: What illustrious or respectable rank does the head of state of the Kingdom of Mercia hold?
SPARQL (Wikidata):  select distinct ?obj where { wd:Q105092 wdt:P1906 ?obj . ?obj wdt:P31 wd:Q355567 } 
Answer: King of Mercia