Hie, i want to confirm that if we post same link again in a single thread, will it be beneficial? From Google's point of view.
It doesn't add any weight to the link, so there's no point in posting several links in the same thread.
There are a lot of variables to consider here. But for link juice purposes it will help just not so much. If the links appeared, let's say weeks apart, and you added new content during that that time you will benefit from that fresh content more than from that link.
It would be useless, even if you posted in a different threads. The link will be counted under one domain / subdomain actually. However, this kind of link is not completely useless. It can help your website to be indexed faster anyway.
Yes, it will helps on SERP in different keyword if use different anchor, this is being used by many people
If you are talking about forums, no it wont help. Forum backlinks are lightweight. i suggest you focus on blog backlinks more.