select * from table where PK >=$yourPK, order by PK Limit 2
Assuming you mean the next PK whose value is greater than the one you know.
however what significance does this next record have???
PK values could be 7,8,9, 19, 45, 82, 83, 90
i.e. there will be gaps due to deletions. and row with pk 19 has no obvious relationship to the row with pk 45.