Is understanding a phenomenon? Buddha says all phenomenon are nonself. If understanding is a phenomenon then my understanding of Dhamma will fade away and I will again fall into ignorance.
So my question is: is understanding a phenomenon?
At least yes, the Dhamma as a stand, or "my" understanding of Dhamma, all stands/views (diṭṭhī) have to be abounded at least, whereas the Dhamma (teching), the raft, will be abounded when having reached the other shore, see the "raft - simile". Note that it is the very last, and in no way good to abound fist or in the middle of the ozean.

Having layed down all views, seeing knowing as unreal as well, one then might reach what is called paññā-vimutti knowing-release, where all kinds of stands or views are abounded, would no more related to.

The word under-stand-ing it self shows well that it is a matter of "holding on it" (upādāna), yet there are Dhammas, there is a Dhamma, that is useable to get free of unreal, insecure (anicca) things.

The first step here is to distinguishing right understanding from wrong understanding: Micchatta Sutta: Wrongness, and after having developed the path completely, one, by abounding it also, gets free of troubles: 


  Among those who live above confrontation
      not pitting view against view,
      whom would you gain as opponent, Pasura,
  among those here
  who are grasping no more?
  
  To Pasura


[Note: This is a gift of Dhamma, not meant for commercial purpose or other kinds of low wordily gains by means of trade and exchange]