“The Guardians of the Galaxy Holiday Special” Groot’s new form was introduced and Mantis (Pom Krementieff) became Peter’s sister. A fan saw the special and asked a question about Knowhere’s purchase by The Guardians. James Gunn (via Twitter): The Guardians purchased Knowhere from The Collector (Benicio Del Toro) after Thanos (Josh Brolin) attacked it in his hunt for The Reality Stone in “Avengers: Infinity War.” They are now working to improve it. Per Gunn “Although the Guardians are sometimes heroes, they work as mercenaries & it brings in a fair amount of money. So after Thanos attacked Knowhere they bought it from the Collector. It was a burnt-out husk & they’ve been rebuilding it.”
The Guardians are known for not being charitable in their heroic acts. Many Guardians want to be paid for their work. Gunn’s response to the fan confirmed that the Guardians now own Knowhere. They bought it after Thanos’ invasion of the galaxy. Knowhere serves as the Guardians base of operations, while the Celestial head/cosmic colony is rebuilt.