Matthew 20:21 James and John's mother asks Jesus that her sons will sit next to Jesus, one on His right and one on His left. Jesus tells them that they don't know what they are asking but then goes on to talk about being "baptized with the baptism that I am baptized with" which (martyrdom) He says they will indeed suffer, but that sitting on His right hand or left is not given by Jesus but by the Father who prepares each of us for it (Matthew 20:23)
In doing a word search, being on the right hand is often mentioned. Do a word search with the Blue Letter Bible or E-sword and see what you come up with. It is a very fruitful study. The left hand is where the goats go to in the sheep and goats judgment (Matthew 25:33) so for mom to ask Jesus to give her sons a place on the right and a place on the left....her request was off track right from the start. This reminds me of the saying "he is my right hand man" (someone that is so helpful you cannot do without him).
He goes on to say that these things are decided and prepared by God the Father. We can ask, but the final decision rests with God.