Ducati's nominal desmo valve clearance specifications, applicable to all desmo engines:

Check clearances with the piston at TDC Compression.

Intake:
opener - .1mm (.004 inch)
closer - NIL to .02mm (NIL to .0008 inch)

Exhaust:
opener - .1mm (.004 inch)
closer - NIL to .02mm (NIL to .0008 inch)

Experience has shown that it's better to leave a little more clearance on the Exhaust opener. And trying to set a zero clearance on the closers is generally hopeless and *always* leads to some binding somewhere. It is much safer to run loose than tight. So the specs I've used for Ducati desmo valve adjustments for the past 25 years are:

Intake:
opener - .1mm (.004 inch)
closer - .025mm to .06mm (.001 inch to .0025 inch)

Exhaust:
opener - .15mm (.006 inch)
closer - .025mm to .06mm (.001 inch to .0025 inch)

Openers are simple: they're like any rocker arm opener setup but you set the clearance with a shim.

Closers take a little more thought. The critical situation for the closing rocker is that it should never be so tight as to try to pull the valve any closer to the valve seat than fully closed. Ideally, you should check closer clearance all the way around the closer cam's circumference (pretty easy to do on a belt drive machine, harder on a bevel driver) to ensure that machining irregularities never allow the closer to attempt a negative clearance around the full cam run.

When to make an adjustment:

If a closer binds anywhere, it needs to be adjusted: aim for .001". If a closer clearance is .003" or greater at the tightest point around the cam, it needs to be adjusted: aim for .001". Otherwise leave the closers alone.

If an opener is tighter than the spec, adjust it to the spec. If an intake opener is looser than .006", adjust it to the spec. If an exhaust opener is looser than .007", adjust it to the spec. Otherwise leave the closers alone.

Always remember that a little extra clearance on any opener or closer is better than too little.

Always remember to check the condition of the closer keeper collets if an adjustment is off: they get beat up over time and can change the clearance. Often times, you can regain the correct clearance by just replacing the collets.