know what (you) are doing

to have the necessary knowledge or experience to do something.

Mountain climbing is a dangerous sport, so I hope he knows what he's doing.

• have mixed feelings about something
• have moments
• have money to burn
• have ... more something than has had hot dinners
• have ... more something than someone has had hot dinners
• have ... more than has had hot dinners
• have ... more than someone has had hot dinners
• have much going for
• have much going for you
• have much time
• have much time someone
• have much time something
• have name in lights
• have name on it
• have name written all over it
• have nose in a book
• have nose in the air
• have nothing between ears
• have nothing between the ears
• have nothing between your ears
• have nothing going for
• have nothing going for it
• have nothing going for you
• have nothing to do with
• have nothing to do with someone