My master who is before me taught me that when the sword is crossed at the middle, I immediately advance forward and take his sword as shown to wound him with a cut or thrust. Also I can injure his leg in the way you see drawn here to hit him with my foot over the back of the leg or under the knee.
The 2nd master of sword in two hands in in Posta Frontale with both hands crossed in the middle. As the 1st scholar, you cut down onto your opponents wrist and then step through to follow with a thrust.
When acting as the second scholar, your counter is conceptually the same. Having beaten your opponents sword offline, give a lateral twist as you enter Posta Frontale to flick your opponents sword that much further away.
Let go of your own sword with your left hand and grab at the point of your opponents sword. Be sure to grab it firmly. Your opponent will instinctively try to pull it away. You will only be cut if you allow the blade to slide through your grip.
Having momentarily immobilised your opponents weapon, you now have a clear line of attack. Make a single handed cut or thrust at your opponent. You will need to step through to get proper distance. Because your opponents weapon is jammed, you are safe to make your attack in false time. Step through first, and drop all your available body weight behind your attack. This will add a degree of power to what will otherwise be quite a weak attack. You are not starting from a mechanically strong position, so take the opportunity to add everything you can to it.
As you step through, Fiore suggests maximising your advantage by kicking your opponents knee. This is explored further by the 3rd scholar.