Generally speaking, you can input accented characters by "touching and holding" a button. And here is the details:
1. Setting Up Keyboards
1.1. Open 'Keyboards' on iPhone: select 'Settings'->'General'->'
1.2. Find 'Norwegian Bokmalål, and change OFF to ON.
2. Input Accented Characters
Open iDict, and select the 'iDict - Norweigan to English (Quick)' or
any other dictionaries you want in the 'Dictionaries' tab.
2.2. Go to the 'Search' tab and touch the search bar. Here comes the keyboard.
2.3. Touch the 'earth' button on the keyboard: change keyboard to 'mellomrom'.
For example you want to check the meaning of word 'døråpning'. Touch
and hold 'o' to input 'ø', and touch and hold 'a' to input 'å'.