ZRH connection time... HELP
 

If I purchase a ticket on Swiss airlines that flies from Milan to Zurich and lands at 1200pm would I have enough time to make a connecting flight on the same airline from Zurich to Chicago that leaves ZRH at 1255?

That is not guaranteed - the slightest delay out of Milan puts you behind the 8-ball, and delays in Malpensa are nothing new. It could work, only just barely, but probably not, even if you get into ZRH on time.

Security (one-on-one interviews before stepping up to the check-in counter), then lining up for the agent at the counter - not to mention the bags not making it onto the plane if you check that late, then the actual TSA-style security at the gate (that's where they do it in ZRH - only gates are secure areas, the concourses are not) - those are all risk factors not in your favor.

If you incoming plane is on time 55min will be enough. If there is a delay of just 15 min it becomes critical. If there is a delay of 30 min forget it. The chance that your incoming plane is late is higher than 50%. And if you miss your transatlantic flight your are in trouble. (The other way round is not that great a problem because you could easily take the next intra-European flights, but the next flight to Chicago will be next day and it will be fully booked.)

Book another connection with at least two, better three hours connection time.

The 1200p flight from Milan to Zurich gets a reality score of 10/10 for on time arrival. So this is not a flight that gets often delayed.
If you want to be on the safe side, try to reserve the earlier flight with Swiss from Milan which arrives in Zurich at 1035a.

This is a pretty tight timeframe.

The problem is that you will almost certainly land at an A gate and have to transfer to an E gate. The walk + train is somewhere between 10 and 20 minutes, depending which gate you land at, how fast you walk, and the timing of the train. Unfortunately, though, you will have to clear security again at Terminal E (unless this changes with the Schengen modifications that are coming in March). The security lines at Terminal E can be anywhere from 2 to 15+ minutes.

So, if things go right and you land on time, you can make the flight. But, it is probably a bit tighter than I would be comfortable with. I would probably do a 75 minute connection, but not a 55 minute connection on this routing.