Do you have the scene with the node who has the script you are working open?
Auto completion, especially for functions like get_node, needs to know which nodes are in the scene and it uses the active/open scene in the editor to check.
Another thing is it could be is that auto completion does not know what type the variable is. Since you are trying to have get get_global_transform and only the signal related functions show up (get_signal_list and get_signal_connection_list), auto completion knows that the variable extends Node, but does not seem to know it extends Spatial.