US keyboard - Danish layout - no @

I got my first Mac two weeks back - an iMac 27". I got great help here and am very grateful for that. Slowly the muscle memory is learning the new layout, but I have one major problem.

I am using a US keyboard where @ is above 2. However, being Danish I shift to Danish keyboard when writing mails etc.

I simply cannot find the @ anywhere on the keyboard. It "should" be with option+2 as per Danish qwerty layout, but it is not.

How can I make a shortcut that works in all applications?

I have tried with the system preferences and keyboard, but apparently my brain is still growing to full Apple size after the switch 😉 and I am still not brainy enough to make it work.

It would be wonderful if say F13 always resulted in a @ on screen in mails, pages, anything really.

It would be preferable if it could be done without downloading third party products.

All input much appreciated / thanks in advance

KAP