1 I find it is difficult to learn English well也正确.I find it difficult to learn English well中it 做形式宾语,真正宾语是后面的动词不定式.I find it is difficult to learn English well中it is difficult to learn English well做宾语从句.
2 I find the book interesting可以加be,也就是 I find the book is interesting道理同上.