Where do I enter the cost of a self published book

[MichaelMc]

If you are inquiring about the costs of editing, photography, etc. that result in a finished manuscript, I would suggest that these are Contracted Labor expenses.

If you are referring to the actual costs of production, leading to the delivery to you of a number of printed, bound copies of the work, ready for distribution, those would be Inventory Purchases. Your inventory remains as an asset until copies are sold, at which time their cost becomes Cost of Goods Sold, and is subtracted from the selling price to determine your Gross Profit in any particular year.