How create an attribute for guidepoint?

Please post code correctly in the forum:

You can identify Sketchup::Drawingelement subclasses by checking and saving a persistent ID between sessions …

Any entity subclass object can have an attribute dictionary created for it …

# At top of Plugin Module
DICT = "YourCompanyName_YourPluginName"

# some where in the code
def add_attr( obj, key, value )
  obj.set_attribute( DICT, key, value )

# Elsewhere calling the method using a ConstructionPoint reference ...
add_attr( cpoint, "Position", cpoint.position )
add_attr( cpoint, "Type", "Start" )