I think that there is no command to do that but don't worry. Do this. Create a file called init.sqs in your mission's folder. Now put in it objective1=false.
Now I assume you have created a trigger or something like that where you will tell that the objective is done ("1" objstatus "DONE" for example). Now in that field add also: objective1=true.
Now, wherever you want to check that, the only thing you should know is that when the objective is completed, the variable objective1 will be true, and when it's not been completed yet, it will be false.