This is the 195th most frequent German word.
liegen
To lie (in a horizontal position).
Here, 'liegen' refers to the state of being positioned horizontally on a surface.
Die Katze liegt auf dem Sofa.
The cat is lying on the sofa.
In this question, 'liegen' is used to inquire about the spatial location or position of an object.
Wo liegt das Buch?
Where is the book located?
In this abstract usage, 'liegen' indicates the cause or reason for something.