What is non-page data structure in SQL Server
From the same source that you mentioned on LATCH_EX


  A latch is a lightweight synchronization mechanism that provides
  synchronization between threads trying to read or change a data
  structure in SQL Server. There are three types of latches:
  
  
  Latches on pages being read from disk (these are covered by the    PAGEIOLATCH_XX wait types – see the PAGEIOLATCH_SH wait type for
  more details)
  Latches on pages already in memory (these are covered by the    PAGELATCH_XX wait types – see the PAGELATCH_EX wait type for more
  details)
  Latches on non-page data structures (i.e. everything else)
  


You are interested in the last part:


  Latches on non-page data structures (i.e. everything else)


Which are latches that do not correspond to data pages in memory or on disk.

Further below in the same source is more information on these types of latches:


  The LATCH_SH and LATCH_EX wait types occur when a thread requires
  access to a non-page data structure (e.g., page buffers in the buffer
  pool (latch type = BUFFER), or the data structure that represents a
  database’s data and log files (latch type = FGCB_ADD_REMOVE)).


With two more examples, waiting on access to page buffers in the buffer pool or data and log file data structures.

An example of accessing the data and log file data structure is shrinking / growing the data or log file of your database.

Your latch type, ACCESS_METHODS_DATASET_PARENT is related to parallellism and latch on the threads needed to acquire scan ranges. More on that here and here.

I would start with looking at the query itself and asking a new question with as much information if the LATCH_EX waits are troublesome for you.