This logical reasoning question involves a coding and decoding type of problem where the names of common items are substituted by different names. Let's decode the given terms step-by-step:

1. The question states that 'pen' is called 'paper'.
2. 'Paper' is called 'book.'
3. 'Book' is called 'table.'
4. 'Table' is called 'chair.'

We need to find out which of these terms we actually use to write on.

Typically, we write on 'paper'. In the coded language given:

• What we normally call 'paper' is referred to as 'book'.

Therefore, in the given code, the item we write on is called 'book'.

Considering the options:

• Option A: Paper - In the coded language, this refers to 'book.'
• Option B: Book - This is the correct answer, as per the logic above.
• Option C: Table - In the coded language, this refers to 'chair.'
• Option D: None of the above - This option is incorrect.

Therefore, the correct answer is Book.