D.
The tonic in D major is D.
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 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!
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.
The dominant note in a G major scale is D. In music theory, the dominant note is the fifth note of the scale, which in the case of G major is D. This note is important because it creates tension and leads back to the tonic note, G, creating a sense of resolution and stability in the music.
The supertonic triad in the key of A flat major is B flat, D flat, and F natural
Chords don't have "tonic notes". Scales do. The tonic note of the G major scale is G (in fact, the tonic note of the X major/minor scale will always be X). Chords do have roots, but that's equally boring: the root of the G major chord is G.
They are basic tonal reference points. Tonic is the key the music is in. Dominant is exactly five whole tones above tonic. This is true of any key. If you are playing in C major, the dominant is G major. If you want to transpose the piece into D major, the tonic is D and the dominant is exactly five whole tones higher - A.
Leading NOTE or the Root note is D#. Leading TONE is D which lies between the sub-mediant and the sub-tonic.
The tonic of the D flat scale is D flat.
The syllable is Re. D is the second tone up from the tonic note, which is C (and do), so it is Re.
The difference is that F major's tonic is F and D minor's tonic is D. Most songs and pieces end either with the tonic of the key signature or a chord with the tonic. Both have a key signature of 1 flat and all the notes are the same except that in D minor the C is raised (incidentally) to C sharp.