Can someone help me identify the chord in the second-to-last measure? For reference, the piece is in the key of C# minor.
As Pat's comment shows, your analysis of V7/V is correct.
In other words, this is a D♯7 chord, meaning that the E♯ and G♯ in the bass are non-chord tones (passing tones, more specifically). What's especially tricky about this chord is the B♯ on the downbeat in the right hand; this is also a passing tone, but it's accented (=on beat one) and lasts twice as long as the chord tone A♯.
Returning to the V7/V analysis, this means that it's actually the V7 of the next chord, which is G♯.
An easy way to spot V7/V in the future is the use of the raised fourth scale degree. Here, that pitch is F𝄪.
I agree this is a V7/V chord. D# major is kind of a made-up chord not found in nature (it doesn't exist in a regular scale due to the F double-sharp.) But it exists theoretically, as seen above. It certainly would look better as an Eb chord, but since it leads to the G# chord, theoretically it makes more sense as a D# chord. The B#, E#, and G# are all accented passing tones.