As an EU/EEA/Swiss citizen you are free to work in Denmark, but you must register for stay of 3 months or more. Citizens from other countries must obtain residence and work permit first. Read details here: https://www.nyidanmark.dk/en-us/coming_to_dk/work/work.htm
Danish Patient Safety Authority. You must hold a Danish Chiropractic authority to practice in Denmark. Depending on your school of graduation this may be granted easily or you may have to take extra classes. When you hold this authority you can work under the licence of another chiropractor, but you cannot work independently. In order to work independently you must complete a one-year paid internship in an existing chiropractic clinic. Ask the chiropractic association (use all of the following as link): http://stps.dk/en/sundhedsprofessionelle-og-myndigheder/autorisation,-anerkendelser-og-selvstaendigt-virke/soeg-autorisation-udenlandsk-uddannet/kiropraktor
ADDITIONAL NOTES:
There is only one chiropractic association in Denmark. While doing your mandatory one year internship (see below) membership of the association is mandatory. After that it is not required. A certain level of Danish proficiency is required. As a Swedish or Norwegian speaker you may qualify.