Horizontal accent marks, that look like '>', go close to the note head in single voice music (c.f. page 9-10 of this style guide). In multi-voiced music, the accents for the upper voice(s) are above the music, and thus are "on top of the stems", and the accents for the lower voice(s) are below.
Where do accents go on notes?
These accent marks appear directly above or below a note head on a piece of sheet music. Any single note value can accommodate an accent, from whole notes to sixteenth notes and beyond. Accents can also occur in any time signature and any musical key.
When should you accent in music?
Accent Emphasis on Beats
Commonly in classical music, accents fall on the primary beats of a measure. For example, in 4/4 time the stress is on the first and third beat of the measure. The less emphasized offbeats are on the second and fourth beats of the measure.