Learn Danish: Har du læst bogen igennem? - Have you read the book all the way through?

In Danish, læse igennem (to read through) acts as a separable phrasal verb. When you include a direct object like bogen (the book), the particle igennem is placed after it. The verb and the particle essentially sandwich the object.

What is the difference between using igennem and gennem in this context?

Igennem functions as an adverb or particle here, modifying the verb to mean doing something completely. Gennem is usually a preposition that needs a noun right after it, like gennem byen (through the town). Because the word stands alone at the end of this sentence, you must use igennem.

Could I use the compound word gennemlæst instead?

Yes! You could say Har du gennemlæst bogen? and it means the exact same thing. However, using the compound verb gennemlæse sounds a bit more formal and is more common in written Danish, whereas læst ... igennem is very natural for everyday speech.

Do I need to add hele vejen to mean 'all the way'?

No, adding hele vejen (all the way) is unnecessary here. When combined with verbs about consuming a text or finishing a process, the word igennem by itself already implies doing it entirely from start to finish.