Without any further specification, the answer would be very simple one: all of the kingdom of the English (former Wessex, East Anglia, Mercia & Northumbria. Cf. ASC: Anglo-Saxon Chronicle MS E (a. 1017)), with a title of king by Cnut the Great (r. 1016-1035) (Cf. Bolton 2017). As I illustrated before in: What was Sweyn Forkbeard's claim on England's crown, and was it at all legitimate by the standards of the day, or was it something of a simple overthrowing takeover?, his father, Sweyn Forkbeard (d. 1014) had also got the kingship of England, probably with the consent of almost all the conquered area in northern and eastern England, but I'm not sure for the western part of England.

The following entry of ASC might be also of interest to consider the wider political influence of Cnut within the British Isles:

• Cnut took a visit in the Isle of Wight (ASC E, a. 1022), not as a part of military expedition.
• The scribe of ASC also record the subjugation of three Scottish rulers, Malcolm, Malbeth (historical core of famous MacBeth), and Iehmarc, to Cnut in the entry of 1031 CE.

References:

• Swanton, Michael (trans.). The Anglo-Saxon Chronicles: New Edition. London: Phoenix Pr., 1996.

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• Bolton, Timothy. Cnut the Great. New Haven: Yale UP, 2017.