No, it is not possible, because the items of an RDD must be serializable and a RDD is not serializable. And this makes sense, otherwise you might transfer over the network a whole RDD which is a problem if it contains a lot of data. And if it does not contain a lot of data, you might and you should use an array or something like it.
However, I don't know how you are implementing the K-nearest neighbor...but be careful: if you do something like calculating the distance between each couple of point, this is actually not scalable in the dataset size, because it's O(n2).
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…