The phrase well-versed means having good knowledge or skill in a subject. This phrase is always followed by the preposition in.
Option A, For, does not fit here. For is used to show purpose or reason, not to show skill in a subject.
Option C, About, is used when we talk about a topic in a general sense, such as talk about English. It does not pair with well-versed.
Option D, With, is used with words like familiar or acquainted, not with well-versed.
The fixed expression is well-versed in, so the correct sentence is I am well-versed in English. The answer is option B, In.