Hello all, I was told that studying PhD should have an excellent memory. I wonder how good memory I should have if I want to have a PhD degree? Do I need to memorize all the thing once I read?

Thank you.

You should avoid seeking further advice from whoever told you that pile of nonsense.
Those who rely on memorising anything soon come up short at one point or another.

My memory is incredibly bad and I still managed to finish my studies :) Remembering important information about your work (e.g., critical papers) comes naturally. You will be talking about these things for three-four years - they will eventually stick. Having said that, in most of my meetings I had to go back to papers and notes to make sure I'm not making false claims, which only made me more careful and thorough. You don't have to memorise anything :)

I 100% agree with pm133 :)