Learn Turkish: Köpek ne kadar süre havladı veya sızlandı?

While ne kadar means 'how much' or 'how long' on its own, adding süre (duration/period) makes it specifically about an amount of time. If you just asked Köpek ne kadar havladı?, it could mean 'How much did the dog bark?' in terms of intensity or frequency. Using ne kadar süre removes any ambiguity and strictly asks for the duration.

The verb sızlandı means 'whined'. Is it related to the word sızlamak (to ache)?

Yes! Sızlamak means to physically ache or throb. By adding the reflexive suffix -n, we get sızlanmak. Instead of a physical ache, it means to 'express your ache' verbally—in other words, to whine, complain, or grumble.

Could I use ne zamandır instead of ne kadar süre here?

Not in this exact sentence. Ne zamandır means 'since when' or 'for how long (leading up to now)', which requires an ongoing action (e.g., How long has the dog been barking?). Because this sentence uses the simple past tense (havladı - did bark), we are asking about a completed block of time in the past. Therefore, ne kadar süre is the correct choice.

Why are the past tense suffixes repeated on both havladı and sızlandı?