How can one check is a man knows well about the drawing?

Give a simple test which needs different skills: Commands, texts, Drawing formats, Dimensionings, Symbols etc. 

Must include drawing reading capability too like Dimensioning, GD & T etc.

Check the same against Time.

Also check for the frequency of using keyboard short cuts for commands.

just let somebody change something in an existing drawing. So they need to understand how the drawing is built up, scales etc. and use the correct layers, works perfect

first of all experience, in the same field as you want to put him,

if you are architect, look for people who have done exactly same thing that project requires like upcoming project is villa,hospital or star hotel etc etc,

Only autocad skills is not enough and it is not just technical skills it is mainly his mental state willingness to work of his own interest career even people have heavy burdens/commitments may not perform well. because they work only for money.