Endless OS supports printers in a best-effort fashion.
Endless OS is based on the Linux operating system, and it is an unfortunate industry reality that printer manufacturers do not provide comprehensive, quality printer support for Linux in a way that is easy to integrate and redistribute. This does mean that Endless OS's printer support is a little hit and miss, and it can be hard to definitively say if a printer will work or not without testing it.
The printers that are most likely to be supported are those that can be connected to your local network (typically via WiFi or Ethernet wired connection) and that can be utilized from an Android or iOS smartphone or tablet. In more technical terms, these are printers that support the Internet Printing Protocol (IPP).
Most network-capable printers released within the last few years fall in this category. Such printers will be automatically detected and made available in Endless OS, with no configuration needed.
Some printers are connected to the PC with a USB cable. Support for such printers is somewhat hit-and-miss. Endless OS will attempt to automatically configure such printers using online resources such as OpenPrinting, but failures are common here, unfortunately.
In general, USB-connected HP printers have the highest likelihood of working, as HP's Linux drivers are generally superior to other brands. However, there are exceptions, notably those HP printers that require the HPLip Binary Plug-In are unsupported; it is not possible to install the required plugin on Endless OS.
Endless OS 4 (unreleased, under development at the time of writing) will add support for IPP-USB printing, resulting in significantly improved compatibility with modern USB printers.
If your printer was not automatically made available, you may wish to try manual configuration.