Katate tsuki and foot work of jodan are for the advanced not for beginners. So if you have just started or have been doing kendo only for 5 years, you don't have to worry about these too much.
A. You can do whatever you want actually. You can block it or parry it.
It does not matter what you do, but it matters what you do after you block or parry.
After you block or parry, it is a very good chance for you to strike your opponent since he/she only has one hand to hold his/her shinai.
Thus, you must think ahead.
What is the best way to block or parry katate tsuki for you to counterattack your opponent?
If you know suriage, kaeshi, osae (pushing down), nayashi (see the article nayasu) and so on, you can use them against tsuki.
I want you to remember one basic rule of footwork in kendo. Basically, when you move forwards, you take a step onto the front foot first.
It does not matter the right or left foot, whichever the front foot, you move that foot first to go forwards. To go backwards, you move the back foot first.
So in Hidari (left) Jodan, which you have your left foot as your front foot, you move the left foot first to go forwards and the right foot to go backwards.
If you are in Migi Jodan, move the right foot first to go forwards and the left foot to go backwards.
Then use okuri ashi, the basic footwork, the back foot never passes the front foot.
In this case, the left foot is the front foot so that right foot (the back foot) never passes the left foot (the front foot).
Hope these help you.