Can my turtle take off its shell?

No. The turtle’s outer shell is made of a thin layer of keratin, like your fingernails. But underneath that layer, there is a layer of bony plates that give the shell its shape. The ribs and vertebrae (backbones) are part of the shell, too. So removing the shell would remove part of the skeleton of the turtle—which is why it is impossible for a turtle to remove its shell.