"There is quite a lot of salt, isn't there?"
It's used to ask for agreement on the matter. It's equivalent to "isn't it?" in English.
結構多い塩ですね。because the subject or the topic is not marked with が or は, the literal translation would be "quite a lot salt is?". In English translates as "It's quite a lot of salt, is it?"
If you put an arbitrary topic or subject on that phrase the consequences are interesting. For instance:
アンチョビは結構多い塩ですね。Anchovies are quite salty, are they?
アンチョビが結構多い塩ですね。It's salt with a lot of anchovies, isn't it?.
私は結構多い塩ですね。I have a lot of salt, haven't I?
私が結構多い塩ですね。I'm quite salty. am I?
And you do not use the question mark in Japanese writing. While in the spoken Japanese is done with a rising intonation as you may expect.
I think it is important to stress that "Question Tags" as translation for this ね usage is highly deliberate in my opinion. That's because only the English language has them and still don't really capture the meaning of ね in the Japanese language. Check my other comment here:https://forum.duolingo.com/comment/32431201?comment_id=35725421
Thank you so much for this comment. I am still very much at the beginner stage, doing Duolingo quite passively and I'm really interested in the kind of distinctions you are writing about. Although I don't know what a "question tag" is. If we are talking about a question mark, ?, then I totally agree. It feels wrong to put it after "isn't it", because you're not waiting for an answer, you're stating the fact that your interlocutor will agree with you, without needing them to actually do it. The very colloquial "innit" (UK only I think?) is perfect in this sense, because really who would bother with a question mark after that. I think it reflects "ね" perfectly. Sadly "innit" can't be used generally as it gives the wrong tone.
けっこう seems to only behave as quite when used with a positive describer, is that accurate? So you could say けっこう美味しいです for quite delicious (btw that's the American quite for the British folks out there, meaning basically the opposite of the British connotation)、but you couldn't say けっこう美味しくない for quite bad. Anyone know if that's true?