Question: My biggest challenge is about synonyms. It is hard to differentiate differences of meanings of synonym words. Even after I consult various dictionaries, some times it is hard to get clarity. In such cases

1. May I ask questions about word differences to the community?
2. If not, what other sources are there to help me?
3. As a non-native English speaker, I can have trouble grasping the meaning. At such times, may I ask the ELU community for more elaboration for any meaning?
4. I’ve noticed that some of users are very good at answering and explaining such questions, but that other users feel these are not good questions. In such situations, may I directly ask the specific user about this question without polluting the site and then give them credit for it once I got answer?

Answer: 
Words have contextual meanings and that is how they need to be studied – contextually. While *correct* is a synonym of *right* in one sense, it is not in other senses of the word.

If you observe and study words according to their contextual meanings, learning synonyms won't be a big challenge. You need to do a lot of reading and listen to people speak in English. Unless you do that, what you pick up from dictionaries won't be of much help. Try building your own sentences with the new words you have learnt. And of course, communities like English.StackExchange.Com are great places to ask questions and clarify your doubts.

So, yes, you can ask questions here and get your doubts clarified. But please search the site and make sure your questions are not duplicates.
I find that questions about synonym differences are very much on-topic here at ELU and not at all General Reference. 

Most dictionaries will give definitions which an educated native speaker can check for correctness of the correct nuance (by the succinct choice of words in the definition), but on the whole **dictionaries do not give a early learners the subtle, or even not so subtle, nuances that are obvious as learned by long time users of the language from prior contexts**. 

That said, your specific main-site questions tend to ask about too many synonyms at once. I think that it is simply a problem with scale; the larger the number of synonyms, the more likely a single answer will be able to answer well, giving rise to legitimate closing by Not Constructive.

Now to answer directly your questions here:

* 1 - Can I ask questions about word differences to the community?

Yes. try to keep the complexity down to 2 or 3 words being compared.

* 2 - If I can not what are the other sources which helps me?

A thesaurus, multiple dictionary lookups (ya gotta do research at some point), and *looking at examples and context to get the nuance*.

* 3 - As a non native English speaker I can have difficulty to grasp the meaning. Such times can I ask community for more elaboration for any meaning?

Yes. Also chat is good for back and forth discussion for elaboration. Also, I find the multi-way conversations there to be very helpful for extricating nuances because people see different sides of the differences.

* 4 - I have experienced some of users are very good in explaining such questions and some users feel these are not good questions. In such situations, can I directly ask the specific user about this question with polluting site and give the credit them once I got answer?

If they answer your question on the Q&A part, SE is already set up to give credit. You can't really give SE upvotes to someone without them already giving an official answer. If you ask otherwise (say in chat), then just thank them, that's credit enough.