The way you would modulate from D major to Bb major would be passing through a D minor chord then modulating to G minor to get to Bb major.
B flat major, with keys B flat and E flat
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.
For c major there are no sharps, for b flat major there are two flats, b flat and e flat
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 fastest method could be a common tone modulation from D-flat to F, which is then the dominant of B-flat. The D-flat moves to C, the A-flat up to A-natural, and the F carries through.
You simply move the key down one half step
The easiest way would be to use a B or B7 chord right before playing E.
B flat Major has 2 flats and G Minor has 2 flats.
D flat major, or b flat minor. The flats are B, E, A, D and G, in that order.
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 IV chord in the key of B flat would be E flat so the triad notes would be e flat, g, and b flat (on keyboard) for guitar it would be e flat, b flat, e flat, g, b flat, and e flat. Played at the 11th fret as a bar chord in standard tuning.
The mediant of B flat major is D.
B flat major, with keys B flat and E flat
B flat Major G minor E flat Major F Major
There are two flats in the key of B flat major: B flat and E flat.
Such a key only exists in theory and not in practice. In C-double-flat major, every single note (C D E F G A B C) would have a double-flat on it, and it would sound the same as B-flat major.