There are different ways to interpret this question.
So let's break this down
John Doe, Diabetes. Obeys every command from the person he knows as
''J'', till he dies.
SO according to rule 23
If you write die of disease like before with a specific disease's
name, but without a specific time, if it takes more than 24 days for
the human to die the 23 day rule will not take effect and the human
will die at an adequate time depending on the disease.
So the first part of your question
John Doe, Diabetes.
works fine and the disease would take a natural course of action.
But here is the catch. You cannot let another person control the user as easily as you think. In the second sentence
Obeys every command from the person he knows as ''J'', till he dies.
You have entered the name 'J' and would kill the person named as 'J' using a heart attack.
Also the line states "Every command" that 'J' gives. SO "every" command could also include that 'J' orders john doe to do things he would not like to do or 'J' could order 'Jon doe' to kill others which is not possible. According to TV tropes
The first is that the Death Note can only kill one person per name. If
it brings harm to anyone else, the person will just die of a heart
attack. Also, aliases don't work, period. The Death Note doesn't know
who L or Kira or Wedy or Aiber or Near or Mello or anyone else with an
alias are. Real names only. However, you could write something like
"Report Siht. Demolishes a hotel, then subsequently dies." and then
write "L Lawliet. Crushed by falling debris as his hotel is
demolished." As long as two names are written, they are able to
So there is a limit of how much you can control and you cannot pass the control to someone else without killing them(since you wrote 'J' in death note already). So you statement in the death note would fail and would kill 'J' with a heart attack and also kill 'John doe' with a heart attack as the "Obeys 'every' command" is ambiguous.
EDIT: In respect to the comment by Dark Yagami.
John Doe, diabetes. Eats fries and gummy bears, cheats on his
would work and you can control them as long as you want (at least till they die of diabetes).
What does not work:
John Doe, diabetes. J, diabetes. John Doe obeys every command of J
won't work. Because you transfer control of power to change the lives of other people (in this case J could ask John Doe to kill someone or make John Doe do something impossible like fly to California from Japan in 2 mins. You cannot give an ambiguous command or control of other people's lives in the Death Note as the death note would just kill John Doe with a heart attack and J with diabetes in the above case.
One thing you guys must understand is, Death Note does not transfer the ability to control the lives of anyone other than the ones in Death Note. So you cannot make someone do something they would never contemplate. So handing over life of someone to another person is impossible for death note to do.