You Do Need power plug adapter while traveling from Sri Lanka to Denmark.

Here is Why You Need An Adapter

The outlet and plug type used in Denmark are C, E, F and K and in Sri Lanka is G. This is how they look like.

Sri Lanka

In Sri Lanka, outlets of type G are in use.

Type G

Denmark

In Denmark, outlets of type C, E, F and K are in use.

Type C

Type E

Type F

Type K