Learn Icelandic: Ég er ekki viss hvort hann kemur. - I am not sure whether he is coming.

No, this is a very common trap! In English, we often use the word 'if' for both conditions ('If it rains...') and indirect questions ('I am not sure if...'). In Icelandic, you must use hvort for indirect yes/no questions. The word ef is strictly used for conditions.

How does the word order work in the second part of the sentence after hvort?

After the subordinating conjunction hvort, the word order stays in the standard Subject-Verb pattern. You just take the normal statement hann kemur (he is coming) and place it directly after hvort. You do not invert the verb and subject like you would in a direct question like Kemur hann? (Is he coming?).

Does the word viss change depending on the gender of the speaker?

Yes, because viss (sure or certain) is an adjective describing ég (I), it must match the speaker's grammatical gender. However, the masculine and feminine forms for this specific word are identical in the nominative case, so both a man and a woman would say Ég er ekki viss. If a non-binary person were speaking, they would use the neuter form visst.

Why is the present tense kemur used here when we are talking about the future?