Learn Turkish: Hep hapşırıyorsun, burnunu silmelisin. - You are always sneezing, you must wipe your nose.

We use the obligation suffix -malı or -meli. For the verb silmek (to wipe), we take the root sil-, add -meli because of e-type vowel harmony, and then add the personal suffix -sin for 'you'. So, sil-meli-sin translates to 'you must wipe'.

I know the word for nose is burun. Why does it change to burn- here?

This is due to a rule called vowel drop. Many two-syllable Turkish words for body parts drop their second vowel when a suffix starting with a vowel is added. So, burun (nose) plus the possessive suffix -un (your) becomes burnun (your nose).

What are the extra suffix letters at the end of burnunu?

Let's break it down! The word is burnun (your nose) plus the accusative case suffix -u. We need the accusative case because 'your nose' is the direct object receiving the action of the verb silmelisin (you must wipe). The full breakdown is burn-un-u.

Could I use her zaman instead of hep for 'always' here?

Yes, you could say Her zaman hapşırıyorsun. However, hep is very natural here because it often means 'constantly' or 'all the time,' which perfectly fits pointing out a repeated habit or a situation happening right now.