Questions & Answers about Laktosen i mælken kan han ikke tåle.
Why is the direct object at the start of the sentence, and why does kan come before han?
This is topicalization. Putting the direct object Laktosen i mælken at the very beginning brings it into focus. Because Danish strictly follows the V2 rule (the verb must be the second idea in a main clause), the auxiliary verb kan takes position two. This forces the subject han to invert and move into position three.
Where does ikke belong when the object is moved to the front like this?
In a main clause, the sentence adverb ikke always comes directly after the subject. Because the topicalized object pushed the subject han into the third position, ikke simply follows right behind it, sitting right before the main infinitive verb tåle.
Why do both laktosen and mælken end with the definite article suffix?
Both laktose and mælk are common gender nouns (en-words). In Danish, you attach the definite article to the end of the noun. Because the sentence refers to the specific lactose inside the specific milk, both get the suffix, becoming laktosen (the lactose) and mælken (the milk).
Is ikke kan tåle the normal way to talk about food intolerances or allergies?
Yes. While the literal translation is that he cannot tolerate or stand it, kan ikke tåle is the most natural and standard phrase in Danish to express that someone is allergic to or intolerant of a specific food, animal, or substance.