Is asking for book recommendations on-topic?
For example, I want to know the best English translation of Yajur Veda done by an Indian author (as opposed to Western authors/translations).
Whether questions about book recommendations should be on topic is somewhat tricky. As @Mr.Allen says, they can invite a opinion-based discussion, since people may have different opinions about what is "best". That doesn't mean that we should necessarily ban it, but there are at least issues to be considered.
In any case, I think what absolutely should be on topic is reference request questions (preferably using a reference-request tag). They're part of the core mission of the site, which is a "Q&A site for followers of the Hindu religion and those interested in learning more about Hinduism." So for example, I think a question like "Are there any complete English translations of the Skanda Purana?" should be within the scope of the site. That doesn't require any opinion or discussion, it's just a purely factual matter of what translations exist, not some subjective evaluation of quality. So whether we decide to allow recommendation question, we should certainly allow objective reference-request questions.
Now as to your particular question, about Yajur Veda translations written by Indians, that seems somewhat problematic to me, not because it's outside of the scope of the site, but because some may think that it presupposes certain controversial attitudes about Indian translators vs. non-Indian translators. On the other hand, a question like "Are there any prose translations of the Ramayana" seems fine to me, because prose vs. poetry is a value-neutral criterion that few would object to.
EDIT: If in addition to translation request questions, which I discussed above, we want to allow pure book recommendation questions as well, then I think some guidelines are in order. The OP should specify what exactly they are seeking to learn, and what their level of background knowledge is. That way the thread doesn't turn into a free-for-all where everyone just lists their favorite book.
An example of an ill-formed question is this one; people thought they should just give whatever Shiva-related books they liked, which is why we got an answer with a recommendation like "Immortals of Meluha." And as you can see, since I didn't know how much the OP already knew about Shiva, my answer contained three possible recommendations based on different assumptions about the OP's background. But if the OP had specified, for instance, "I've heard that Shiva is the Hindu god of destruction; where can I learn some basic facts and stories about him", then we would have a clearer idea of what kind of book would be an appropriate recommendation. That way, even if there's some subjectivity about the quality of a particular book, we can at least judge how well it meets the OP's needs.
If we go through close vote reason the we can clearly see "opinion based are off topic".
So why to allow question which are obvious "opinion based".
Now we have another version of this kind of question, where user want a translated copy of specific mythological books. Refer this two
Don't worry more coming soon. Then we will have to search for french, Chinese, Japanese and all kind of language version of all Indian mythological books.
So do we want to kill the seed of trouble or we will handle grown up big tree of trouble later.