Hi, I'm a fairly new user, trying to find a way to iterate over the attributes on a given point or prim in python.

Or at the least, determine if a given attribute exists. Any advice?

Attributes are strictly linked to the geometry, so you want to search through the hou.Geometry() class
https://www.sidefx.com/docs/houdini/hom/hou/Geometry.html [www.sidefx.com]

You'll find both methods for retrieving the list of attributes and for checking the existence of a specific attrib;

https://www.tokeru.com/cgwiki/index.php?title=HoudiniPython#Get_point_attributes_from_a_node [www.tokeru.com]