You will not normally be notified, you just have to remember the date on which the Conditional Discharge was imposed and count the months/years from then on. Remember, if you commit an offence during the duration of the CD, you will be re-tried for the orignal offence. Good luck! If you really cannot remember, telephone the Court at which you appeared and they should be able to trace you through their records.
Unless they were convicted and sentenced in their absence the person in question would not receive any documentation confirming the court's decision as suggested by paraffin.
With matters such as suspended sentences, conditional discharges and driving disqualifications, sentence is announced and defendants are expected to take note of the relevant dates.
For this very reason, such sentences (including conditional discharges) are not normally passed down in the absence of the defendant as the judge or magistrates need to be sure that the defendant understands the implications of their sentence.