Can i deduct ink for my printer if it is used for printing of business only and do not have an office? How do i prove which percentage is for business printing only?

Yes, you can deduct the cost of your printer ink.  The percentage of business printing will be based on the amount of time you spend on doing "business" activities. To prove this expense just make sure that you keep your receipts and document the amount of printing that you typically do going forward.