Learn Icelandic: Er maðurinn veikur?

This is how you ask a yes/no question in Icelandic! You simply swap the subject and the verb. A regular statement is Maðurinn er veikur (The man is sick). By moving the verb er to the front, you create the question Er maðurinn veikur? (Is the man sick?).

Where is the word for 'the' in this sentence?

In Icelandic, the word for 'the' is usually attached to the end of the noun instead of being a separate word. The base word for a man is maður. By adding the ending -inn, it becomes maðurinn (the man).

Why does the word for sick (veikur) end in -ur?

Adjectives in Icelandic have to match the gender of the noun they describe. Because maður is a masculine noun, the adjective takes the masculine singular ending -ur. If you were asking about a woman, the adjective would drop the ending and you would ask: Er konan veik?

If I want to ask 'Is the man not sick?', where does the word for 'not' go?

The word for 'not' is ekki, and in a yes/no question like this, it goes right after the subject. You would say: Er maðurinn ekki veikur?