Find book reviews in magazines/journals - for non- literary books
A good beginning place might be this database that covers reviews of all types of books: Book Review Digest Plus.
Other good general databases are: Academic Search Complete and MasterFile Premier, but there are many others.
If your book is a popular one and it was published after 1981 you might check the online version of the Books section of the New York Times for book reviews. Books published between 1850 and 1981 may be review in the New York Times Historical database.
If you do not find what you want in it, check another database listed here or contact a librarian.
How to find reviews of literary books
For literary works check under this section for literature databases such as Literature and Literary Criticism