Is it permissible to direct (people) to a book offered for sale online merely by knowing its title, which does not deal with forbidden matters? Is it sufficient to only review the title? And what if its title deals with a permissible matter, but its content inside is forbidden?

The presence of a book for sale on the internet constitutes a promotion for it. If the book calls to good, then it is a promotion for good, and "the one who guides to good is like the one who does it." If it calls to evil, then it is a promotion for evil, and "the one who guides to evil is like the one who does it." Therefore, it is not sufficient to merely ensure that the book's title does not address forbidden matters; rather, it must be verified that it does not promote anything forbidden.