should as "obligation" or "presumption"

As "must" can be used either as "obligation" or "certainty", I think "should" can be used as either "obligation(less strong than must) or "presumption(about 70%), but does it all depend on context and common sense to determine if "should" means "obligation" or "presumption" like in the following?

gz64
1. You've worked at this company for ten years. You should know who Mr.Smith is.
- Can this "should" be interpreted as "obligation" or "presumption"? Is it ambiguous?

I'm sorry, I removed one question to unburden you.

My temporary conclusion is this can be interpreted either as obligation or presumption depending on the context.
If you have any opposing opinion, please let me know.

You should know who Mr.Smith is.

How can you obligate someone to know someone?