What is the fruit generally called which Adam and Eve ate?

Answer 1

Many people refer to it as an apple, but it is not actually known if it was a fruit known to us today. The Bible itself does not call it an apple. It is referred to as the fruit of 'the tree of the knowledge of good and evil.'

Answer 2

It's often described as an "apple" but that's just a figure of speech for any kind of fruit. The actual command is to avoid the fruit of the tree of the knowledge of good and evil. It's pretty likely that there was just one tree that fit that description, so the Forbidden Fruit is unlikely to be available today.

Of course, many regard the Garden Story as an allegory for mankind separating from the innocence of the animals by coming to appreciate morality and in consequence, disobedience. In that context, even the idea of "eating fruit" must be interpreted symbolically.