Compare these two sentences:
"He jumped from the bus"
and
"He jumped off the bus"
With this one:
"He jumped off of the bus"
Compare also this:
"Where is Bob?"
With this
"Where is Bob at"?
The latter examples are mostly favored by Americans.
Are the prepositions in the latter examples unnecessary?
All three of your bus examples have prepositions -- from, off, and of, respectively:
He jumped from the bus
He jumped off the bus
He jumped off of the bus
Each one, however, has a slightly different meaning. All three indicate that he jumped, but then add answers to different questions. The first adds the answer to from where did he jump? The second is similar but answers the question which way did he jump, off or on? The last one says he jumped off, and then answered the question what did he jump off of?
So, while the of in your last example isn't strictly necessary, it adds more information.
When it comes to Bob and his location, your second example is, as Yosef mentioned in his comment, definitely slang and would not be acceptable in a professional or academic setting, unless the speaker added more context, such as where is Bob at in relation to marriage equality? or where is Bob at in reading that book?
It could be used on its own if the conversation had already provided the context:
Sally: I know Margaret is in favor of it and Pete is leaning towards saying yes.
Henry: Where is Bob at [on the topic at hand]?
Other than that, the simple "Where is Bob at?" referring to Bob's location is, at best, informal.
(Note that the equally unpleasant Where you at? is also common here in the US and should be avoided at all costs; it can be replaced with Where are you?)
