hook_node_load for currently viewed node?
It depends on when and where you trying to modify the $node. hook_node_load runs every time a node is loaded,whereas  hook_node_view runs only when a node is about to be rendered on the page. 

The reason you might not be having the node id in question in you hook_node_load may be because the context in which you are calling hook_node_load might be wrong.
In order to test you can create a dummy callback and call the node_load() in it with you nid in question. You can see that once you call the node_load() api, it will invoke a call to hook_node_load.

Cheers