Changing a field title in a panel
You can use keywords from contexts when you override a title of a pane in Panels. Go to Contexts in the Page Manager UI. The summary of contexts displays the available keywords. 

In your situation you may want to add a new context, the node that you want your pane title to be pre-populated from. You can select the node ID, and the same node will always be loaded.

If it's not always the same node that you want to use, but e.g. a reference field in your already loaded node defines it, you can use a relationship to create the appropriate node context.