I've learned this piece many years ago and decided to play it this morning (thanks to Russell who wanted some guidance on learning it).
There are 10 subject entrances in this fugue:
1. (page 1-system 1- measure 1) Subject in G major, tonic, tenor.
2. (1-2-4) Answer in D major, dominant, alto.
3. (1-5-4) Subject in G major, tonic, soprano.
4. (2-2-2) Answer in D major, dominant, bass.
5. (2-5-2) Subject in B minor, relative minor of the dominant, tenor.
6. (3-4-2) Subject in E minor, relative minor, alto.
7. (4-2-2) Subject in G major, tonic, bass.
8. (4-3-4) Answer in D major, dominant, soprano.
9. (4-5-3) Subject in B minor, relative minor of the dominant, tenor.
10. (5-3-1) Subject in G major, tonic, bass.
This time, when I played it, I looked at this fugue with the fresh eye and tried to imagine the difficult places for many organists:
1. (1-2-2) Play a mordent on the beat starting with the main note.
2. (1-5-4) Don't forget to take on the first beat the alto and the tenor parts with the left hand.
3. (2-2-2) Prepare in advance for the pedal entrance.
4. (2-2-2 to 2-3-1) Active pedal part - difficult movement with the right foot.
5. (2-4-1) Additional tenor part - don't miss it.
6. (2-5-1) Active pedal part approaching the cadence in B minor.
7. (3-4-2) Active left hand as well as the mordent in the right hand (start from the upper note on the beat).
8. (4-2-2) Prepare for the pedal entrance in advance. To avoid damaging your knees, your lower body should be facing the high pedal notes and the upper body - looking straight.
9. (4-2-2 until the end) Extremely active pedal part. In descending pedal lines, push off with the right foot and in ascending pedal lines, push off with the left foot to change position on the pedalboard.
Here's the score for printing, if you want to play it. Don't forget to use articulate legato touch and aim for a slow tempo because pedal entrances will not be easy. Play separate parts, if you are a beginner. Feel free to use a secondary softer manual for echo passages (notated - p).