"you should know how to do it by now"

Question

How to render the English should when in the sense of "it is expected" rather than hortatory command or "it behooves". Examples to illustrate the meaning I'm looking for:

A: "What it the next step?
B: "Why are you asking? you should know it by now." [or rather "you should have known"]

After one year of studying, students should be able to read Cicero (should "know how to..."/"know")

It seems other languages use basically the same phrase for hortatory and expectation, which indeed makes sense, but for some reason I doubt it works in Latin as well:

iam necesse tibi est scire quomodo ...

My feelings, it implies harsher tone then what I'm for. and if that's proper, should the infinitive be in the perfect?

Other option I'm thinking is using the gerundive, but I suffer the same doubts:

(iam) tibi erat sciendum

Maybe there is a different formulation better at least for the future? (second example above), or to resort to "necesse fuerit"?

Answer 1

I suggest using the verb debere. It can be used for various kinds of owing, including "owing to do something". It expresses a must of expectation, not an order — although an order can of course be veiled as a polite remark.

For example:

You should know it by now.
Iam scire debes.

Answer 2

If you want to specifically say "You should know how to do it by now" rather than "you should already know", you may want Id agere iam scire debes (or, if the "doing it" is a physically constructive act like building a chair as opposed to, say, filing a motion, Id facere iam scire debes).