Could you help me?
I have a question about the following essay.

My grandmother had a beautiful elephant carved out of sandalwood on her dressing table which I secretly used to covet. One day my sister said “Oh Grandma, please can I have it?” and, to my fury and disbelief, she just gave it to her! Ever since I have been scouring the world. I have rummaged round junk shops and antique shops all over Europe.

(Skip)

……but as usual there was that niggling feeling that my collection, not matter how valuable, would never be complete. Not without my Grandmothers elephant! What a waste for it to be with my sister when it could be, should be, with me!(*1) “Oh well, never mind, try not to be obsessed” I told myself.

Collecting things - My Grandmother's elephant By Chris Wilson
http://learnenglish.britishcouncil.org/en/magazine-articles/

(Question) What is the meaning of the following sentence: "What a waste for it to be with my sister when it could be, should be, with me!"

Question

Could you help me?
I have a question about the following essay.

My grandmother had a beautiful elephant carved out of sandalwood on her dressing table which I secretly used to covet. One day my sister said “Oh Grandma, please can I have it?” and, to my fury and disbelief, she just gave it to her! Ever since I have been scouring the world. I have rummaged round junk shops and antique shops all over Europe.

(Skip)

……but as usual there was that niggling feeling that my collection, not matter how valuable, would never be complete. Not without my Grandmothers elephant! What a waste for it to be with my sister when it could be, should be,  with me!(*1) “Oh well, never mind, try not to be obsessed” I told myself.

Collecting things - My Grandmother's elephant By Chris Wilson
http://learnenglish.britishcouncil.org/en/magazine-articles/

(Question) What is the meaning of the following sentence: "What a waste for it to be with my sister when it could be, should be,  with me!"

Answer

"What a waste for it to be with my sister when it could be, should be, with me!"

It's a rude sentence, but a little funny at the same time. The writer wants the carved elephant and feels envious that her sister has it. 'could be' implies 'I could have the elephant, and 'should be' implies that the writer really wants it... almost like she has to have the elephant or she will die.

"What a waste for it to be with my sister 
그건 안타깝게도 우리 동생의 것이다.
 
What a => 이런, 어머, 등등 'What a nice voice she has!' 세상에..... 걔 목소리가 정말 좋으네요. 'What a rude child you are!' 어머, 너 정말로 무례한 아이구나! 
waste => 안타까운 거, 쓰레기, ... 등등
it to be with my sister => 동생이 가지고 있다는 뜻이에요  with은 원래 '함께'라는 뜻이지만, 여기서 '뭔가가 동생의 것'이라는 뜻이에요.

[when] it could be, 
[when]은 여기서 가능성이나 희망을 나타내요. ... 흠, 설명하기가 좀 힘드네요.
It could be, should be, with me!
내꺼 될 수도 있겠네.... 아니.... 처음부터 내꺼야 하는데!