Regarding Yash’s question: “.. how one can know whether he has attained the sakadagami Stage?”
One will know that when one has lost the desire to POSSESS (own) material things that provide sensual pleasures. For example, houses, cars, paintings, …
But a Sakadagami has not yet REMOVED the tendency to enjoy such things.
– A Sakadagami needs to keep contemplating the “anicca nature” of such sensual pleasures.
– One WILL know when one gets there. One will not have the same tendencies to accumulate worldly possessions.
We discussed the key ideas in the thread on your question on the Anagami stage. You may want to re-read that. Until one starts giving up the craving for sensual pleasures, one is away from both Sakadagami and Anagami stages.