A) If I have a sentence like this:
"He suggests that she buy this book.",
how should I transform it, if the action happened long ago?
I have two versions but I am not sure about them:
1) In 1905, he suggested that she buy that book.
2) In 1905, he suggested that she should buy that book.
B) I know I can not say "He suggested to her that she buy the book.", but how can I stress the fact that the suggestion was made to her and not in general?
Both of your example sentences are perfectly fine. In fact the subjunctive clause is completely independent of time, and the actual temporal context can only be determined from the rest of the sentence:
She should buy the book.
He suggests that she should buy the book.
In the past, he suggested that she should buy the book.
In the future, he is going to suggest that she should buy the book.
This works the same if you remove the "should" (although in this case it's no longer a subordinate subjunctive clause).
In the past, he suggested she buy the book.
In the future, he will suggest she buy the book.
[1] In 1905, he suggested that she buy that book.
[2] In 1905, he suggested that she should buy that book.
They are both okay; just two different ways of saying the same thing, really.
Your example [1] involves the use of the ‘subjunctive mandative’ where the subordinate content clause uses a plain verb-form.
By contrast, [2] is a "should-mandative" construction which has a special use of the modal auxiliary verb should. It is not actually a subjunctive, though it is equivalent in meaning to the subjunctive in [1]. The should-mandative is more common in BrE than AmE, where the subjunctive mandative is generally preferred.
