The tonic of the D flat scale is D flat.
The tonic note of any diatonic scale is the first note (starting note) of the scale. In the case of G-flat major the tonic note is G-flat!
Relative major and minor share the same key signature but a different tonic note (a tonic note is the first note of the scale or in solfege tonic is DO). For example, D flat major has five flats in it's key signature and b flat minor has 5 flats in it's key signature; therefore, D flat major and b flat minor are relative.
The supertonic triad in the key of A flat major is B flat, D flat, and F natural
You can call it different things depending on your need. The second note is the supertonic, the full step just above the tonic. The tonic names the scale. In solfege the second note is Re (recall the song from The Sound of Music: Doe, a deer, a female deer...) Also, the second note has a specific name if you name the tonic that the scale starts with. In the scale of C, the second note is D, for example.
It is a major chord. Actually, tonic is simply defined as the first note in the scale or key. All chords have tonic note. The tonic of a C chord is the C. The tonic of a C minor chord is a C. The tonic of a C minor major 7 is a C.
F is the tonic. Therefore, from supertonic (the second note) to supertonic is G, A flat, B flat, C, D flat, E natural (a harmonic minor scale has the 7th note raised), F, G.
To determine what the seventh note (leading note) is in a minor scale, you need to determine which minor scale you are playing. The seventh note of a natural minor scale, you take the note which is a whole tone (2 notes) below your tonic (the note which is the name of your scale). Example: In A natural minor scale the leading note is G. The seventh note of a harmonic minor scale is a semitone (1 note) below your tonic note. Ex: In E harmonic minor scale, the leading note is D sharp. The seventh note of a melodic minor scale (ascending) will be a semitone below your tonic note, like your harmonic minor scale. Descending the melodic minor scale reverts to its natural state, therefore your seventh note will be a whole tone below your tonic.
B flat note, C note, D note, E flat note, F note, G note, A note, B flat note.
Leading NOTE or the Root note is D#. Leading TONE is D which lies between the sub-mediant and the sub-tonic.
The mediant is the third note of a scale so the mediant of D flat is E
D
E