I have this confusion all the time, I see people posting some questions which aren't exactly duplicate to other questions on Stack Overflow but with a little google search, the answer can easily be found on stack overflow for those questions. So should we answer those questions or flag them?
If you have the rep, vote to close as an exact duplicate. If you don't, put a comment pointing to the duplicate, and others will pick it up and VtoC (I think this will be just as quick as flagging for a moderator, depending on how niche the subject matter is). Repeating the same answers doesn't really help anything, even if you repeat all of the answers and all of the comments. This just splinters the knowledge. Keeping the duplicate question closed can be helpful if the wording or content is significantly different (it can direct users to the same answers even if they used different search terms).