Which is better: to supplicate after rising from the rak'ah of witr, or after the taslim, for one who woke up before Fajr, prayed, and wished to supplicate to Allah?

Supplication is prescribed after concluding the prayer, whether it be obligatory or supererogatory. The Prophet, peace and blessings be upon him, supplicated after supererogatory prayers. It is preferable to combine supplication both during and after the prayer. However, if combining them is not possible, then supplication within the prayer is better than supplication outside of it, for supplication during prayer is more likely to be answered than at other times.