i came across a weird chord, D/A. but is the root note of this chord D or A? A is being played as a bass and is lower.
The root of a chord is not always the same as the lowest sounding note. When the lowest sounding note is the root, we say the chord is in root position. When it's not, we say the chord is inverted or is an inversion.
Chord names with slashes are inversions. In this case, the lowest sounding note is A, but the root is still D because the rest of the notes are D and F#, and D F# and A form a major triad with a root of D.