This has not been implemented -- you might consider filing a feature request at https://github.com/rstudio/rstudio/issues.
This is usually done via the "fuzzy finder", with Ctrl + .. Note that this navigates both function definitions as well as files located in the active project.
Lines and be commented + uncommented with Ctrl + Alt + C.
There isn't a preset keybinding for this, but you could add your own keybinding via Tools -> Modify Keyboard Shortcuts, with a binding for the Insert Chunk Python command.