Normally, when you request the history of one versionable, you would get an ChangeHistoryEntry[] entries (array).

ITeamRepository repo; // you should have this already
IAuditableClient audCli = (IAuditableClient) repo.getClientLibrary(IAuditableClient.class);
for (ChangeHistoryEntry changeEntry : entries)
{
  ICangeSetHandle csh = changeEntry.getChangeSet();
  IChangeSet cs = repo.itemManager().fetchCompleteItem(handle, ItemManager.DEFAULT, monitor);
  IContributorHandle conHdl = cs.getAuthor(); // this would get you the author. Only the handle though. You need to resolve it as below
  IContributor con = audCli.fetchCurrentAuditable(conHdl, .......... )
  cs.getLastChangeDate(); // get the change time stamp
  cs.getComment(); // get the comment
}