J'oublie
This is the present tense of the verb "oublier" (to forget).
Here are some other ways to say it, depending on the context:
* J'ai oublié (I forgot - past tense)
* Je vais oublier (I am going to forget - future tense)
* J'oublierai (I will forget - future tense)
* J'oubliais (I was forgetting - imperfect tense)
* J'avais oublié (I had forgotten - pluperfect tense)
You can also use expressions like:
* Je ne me souviens plus (I don't remember anymore)
* Ça m'échappe (It escapes me)
* Je l'ai perdu de vue (I lost track of it)