When dealing with personal pronouns, the negation may be placed either directly after the verb, or after the following pronoun. Beware that there is a difference in meaning between the two:
"Kona mi elsker meg ikke" = "My wife doesn't love me." - her feelings changed/were never there.
"Kona mi elsker ikke meg" = "My wife doesn't love me." - but she does love somebody else.
It's the difference between your wife not feeling any love for you, and your wife loving someone else instead of you.
Try reading the two English sentences out loud, and stressing the bolded word each time. See if the meaning changes for you.
These things are much easier to grasp in context than they are in short Duolingo sentences, so don't worry too much about it if it still doesn't click.