b flat, c, d, e flat, f, g, a, b flat
The subdominant in a scale is the 4th, which in the key of B-flat major is E-flat.
Eb Major
The dominant note is the 5th note in the scale. In the B Major scale, F is the dominant note.
G-flat major scale has the most with 6 flats: b-flat, e-flat, a-flat, d-flat, g-flat, and c-flat.Of course, one could argue that other scales have more flats (such as C-flat major, F-flat major, B-double-flat major, etc), but these scales are typically notated as their enharmonic equivalent (e.g. A major instead of B-double-flat major).
The major scale with three flats is the E-flat major scale. The key signature for E-flat major consists of three flats: B-flat, E-flat, and A-flat, arranged from left to right on the staff. The scale ascending from the first degree (E-flat) is E-flat, F, G, A-flat, B-flat, C, D, and returns to E-flat.
The subdominant in a scale is the 4th, which in the key of B-flat major is E-flat.
The mediant of B flat major is D.
B-flat
Eb Major
The B-flat major scale contains two flats: B-flat and E-flat. However, if you're looking for a scale that has only one B-flat, it would be the G minor scale, which is the relative minor of B-flat major. In G minor, the B-flat appears as the sixth scale degree, while the scale itself includes B-flat as part of its harmonic and melodic variations.
A-flat Major scale
Your question doesn't make much sense. But for any scale, "do" would be the first note of the scale, which is whatever the scale is called. But for a flat major, from what it sounds like you're asking, the note would be a flat. Ex: In B flat major, "Do" is b flat.
The mediant is the 3rd of the scale, so in B-flat it's D.
B flat C D E flat F G A B flat
F Major
Eb Major
the scale e flat major has a flat, b flat and e flat.