/track (player)

As soon as you type this, it will show everything the player does, from adding and destroying blocks to typing invalid/valid commands. I have some ideas as to what the command could show.

Blocks added: Single command = /tba (player)
Info will be shown as: (player) placed (block)
When you type this, it will bring up a list every 3 seconds (until your turn the command off) showing the blocks he/she places when you type the command.

Blocks destroyed: Single command = /tbd (player)
Info will be shown as: (player) destroyed (block)
When you type this, it will bring up a list every 3 seconds (until your turn the command off) showing the blocks he/she destroys when you type the command.

Valid/Invalid commands: Single command = /tvic (player)
Info will be shown as: (player) typed or tried to type (command)
When you type this, it will bring up a list every 3 seconds (until your turn the command off) showing the commands he/she types despite if the command is valid or not when you type the command.

Which world he is in: Single command = /tl (player)
Info will be shown as: (player) is in (world)
When you type this, it will bring up a list every 3 seconds (until your turn the command off) showing which world he/she is in when you the command.

Notes:
By typing the same code again, it will turn the tracking off. You can type several of the single commands, just to see the ones info you want displayed.
By typing /tracking_off, it will turn off all the tracking commands you have running.
I advise that if this command be put in place, it shall only be accessible if your ranked HOP+
I also advise that if this command be put in place, you should also think of other ideas since i only gave some basic ideas that you probably would have though of

Highlight pretty much already does the first two commands as in it shows every block edited by a user in the time between you typing the command and the time-scale you specify.

Seeing which command a user last used is the job of the /last command. To be honest I can't see much need to see which commands they use every 3 seconds, even in the unlikely event that an op needed to see which command was used for whatever reason the server logs all commands used by all players and Ops+ will soon have access to these logs.

The world command every few seconds would read something like this,
[user] is in guest
[user] is in guest
[user] is in guest
[user] is in guest
[user] is in guest
[user] is in guest

And basically just spam the operators chat with the same message, and if we need to know it to that extent just using the /whois or /players commands would be more than enough I think. Plus we do already have ways of following an individual user and seeing everything they see without them knowing anyway.

Moved to HawkServ suggestions since they're commands.