Add spaces: Troubleisaboy'smiddlename.Selectfourtoolstostartsometrouble.

Answer: Trouble is a boy's middle name. Select four tools to start some trouble.

Add spaces: TheDanishscholar,NielsLukman,elaboratedin1943inhisdoctoralthesisonthetheorythattheHerulsbecameearlsintheDanishkingdoms.

Answer: The Danish scholar, Niels Lukman, elaborated in 1943 in his doctoral thesis on the theory that the Heruls became earls in the Danish kingdoms.

Add spaces: TheRoyalDanishCollectionRosenborgTheCastleInteriorandobjects2ChristianIV'sWritingRoomChristianIV,1585

Answer:
The Royal Danish Collection Rosenborg The Castle Interior and objects 2 Christian IV's Writing Room Christian IV, 1585