This is really off-topic for this site, but let's have a go anyway.

You need to join the BookAuthor table with itself. I'm old-skool so I do joins in the WHERE clause, but there's probably a simpler way to do it using an explicit JOIN clause.

select a.book
from BookAuthor a, BookAuthor b
where a.author = 'Smith' and b.author = 'Jones'
and a.book = b.book;
[download]

Update: The JOIN syntax looks like this:

select a.book
from BookAuthor a
inner join BookAuthor b
on a.book = b.book
where a.author = 'Smith' and b.author = 'Jones';
[download]

You should be able to omit the "INNER", but I was testing on a rather old version of MySQL which didn't support the abbreviated syntax.