Do I need to take Vitamin K2 if I’m already taking Vitamin D3?

In many cases, taking K2 with D3 would be beneficial .. however it does depend on your diet.

Vitamin D increases calcium absorption & K2 helps direct that calcium into bones instead of accumulating in the arteries.

So it's often recommended to take Vitamin K2 if you're also supplementing with Vitamin D3 ... unless you're already getting enough through foods rich in Vitamin K2 like natto, chicken thigh, egg yolk, some cheeses (Gouda, brie, edam), grass fed butter.