关于in one’s opinion

in the opinion of me
如果是in the opinion of mine
那就是in one's opinion=in the opinion of one's了

in the opinion of mine

in the opinion of sb 这里Of 表示一种所属关系。而mine 本身就有所属关系的意思。所以这里应是in my opinion= in the opinion of me

语法搞死人 谁会去说in the opinion of me/mine ？

你就说 in my opinion, in my point of view

in the opinion of sb不要研究这个，似乎没见过这种说法
老外常说的是：from my point of view/from where I stand/I'd say if you ask/I'd always support the idea that....诸如此类
要学就学原汁原味的

in the opinion of me 还是in the opinion of mine 还是in the opinion of I？

都不是， 英语没有这些说法的