Q: How do I print from my iPad to wifi printer, without computer

It would have to be connected to the same Wi-Fi network as the iPad, and the printer has to be either AirPrint compatible, or there has to be an app on the iPad that supports that particular printer brand and model.

About AirPrint - Apple Support

In addition to Chris' suggestions, look on your printer manufacturer's web page. Some have apps, there are also third party printing apps that will work with wifi printers (I used print n share), and some also have their own work arounds, such as using google documents to print.