At/In My Job?

Well, it is 'job' that sounds a little odd there:

There are a lot of strange people in/at my office/workplace.

Now both prepositions sound reasonable.

MeggPhaggSiouxWhich one is more appropriate?

If you leave it as is, at is better, but what I hear more often is "There are a lot of strange people where I work". The strange people aren't really at your job. Only you are at your job.

CJ

So,

"There are a lot of strange people at my job." is the most accepted version, and

"There are a lot of strange people in my job." is wrong under all circumstances?

You might say "There are a lot of strange people in my job" if you were, for example, a mortician, and you wanted to comment about the other people in the world who perform the same job for a living, although in that case it would be more usual to say "There are a lot strange people in my line of work".

Making slight changes:

a. "I work long hours at my job."

b. "I work long hours in my job."

Could b. be also wrong?

No, that's OK.

Megg is incorrect. You can say this:

In my job I have many responsibilities.

I have many responsibilities in my job.

Here we are talking about your actual job, and not the place where you work.