The “classic” recording position is about 40 cm above the 12th fret (which is where the neck meets the guitar body).
The best position for this player with this guitar in this room playing in this style with this microphone … may well be different.
There is a very good article here: http://www.soundonsound.com/sos/aug01/articles/recacgtr0801.asp (which is where the picture came from)
There was some discussion about techniques for recording acoustic guitar in this thread: https://forum.audacityteam.org/t/i-get-a-watery-sound-when-removing-noise-in-audacity/15094/76
as well as the prize winning “longest thread on the forum”: https://forum.audacityteam.org/t/budget-usb-mic-for-classical-guitar-recording-needed/12367/1