We don't see enough of Harry's classmates to determine for sure.
We only really know about students who interact with Harry somewhat regularly. The second smartest in Harry’s year could be some Ravenclaw who Harry's never talked to, so wasn't even mentioned. It could also be a secondary or minor character who was mentioned by name but that we don't know a lot about, like Susan Bones. Susan could be a genius for all we know, but it didn't matter to Harry, so we wouldn't know.
But, out of the ones we do know, it could be Draco.
Out of the students we do have a lot of information about, only a few of them have a chance of being the second smartest. Harry and Ron slack off far too much for them to be considered second smartest. None of the other Gryffindors in Harry's year seem particularly intelligent, so I doubt it's any of them. It's definitely not Crabbe or Goyle.
The only student who we consistently hear does well in class is Draco Malfoy (well, except for his sixth year). Draco might have been stuck-up, but he was always shown to be intelligent, probably more than most other students. One example of this was that he was able to figure out how the Vanishing Cabinet worked by himself, mend it, and use it as a pathway to Hogwarts.
“Everyone thought it was a really good story, but I was the only one who realised what it meant – even Borgin didn’t know – I was the one who realised there could be a way into Hogwarts through the Cabinets if I fixed the broken one.’
‘Very good,’ murmured Dumbledore. ‘So the Death Eaters were able to pass from Borgin and Burkes into the school to help you … a clever plan, a very clever plan … and, as you say, right under my nose …”
- Harry Potter and the Half-Blood Prince, Chapter 27 (The Lightning-Struck Tower)
He was also able to learn Occlumency, as well as nonverbal magic. In addition, he would have likely applied his intelligence to his class work. Draco wanted to make his father proud and not disappoint him, so he would probably have cared about his grades.