Is it possible ～ておく in continuous state (～ている)?

Question

I'm curious now since I read in Tae Kim's Guide that ておく means to prepare/do something for the future.

So for example, if one is currently in the progress of studying for the future would it be this?

勉強しておいている

Answer 1

Though there is no hard rule to prohibit using ておく and ている together, it'd sound as unnecessarily mouthful as saying "have been being" in English. Even when you utter it, you cannot make this ている have "progressive" sense, but only "perfect".

勉強しておいている ≈ I have had my study (for future) done

ておく is a part of grammar that carries resultative aspect, and you cannot focus its result and process at the same time.

So for example, if one is currently in the progress of studying for the future

you should instead use the word that means "in advance":

あらかじめ勉強している

Answer 2

「勉強{べんきょう}しておいている」 sounds fairly wordy, awkward and unnatural. IMHO, practically no native speakers would actually use it.

If anyone ever said it, it would sound as if he were unsure if a test would actually take place at all. Even in that situation, it would still sound quite unnatural.

It should just be just 「勉強している」 or 「勉強しておく」.

For the phrase 「Verb + て + おいている」 to sound natural, the verb would generally need to describe an instantaneous action and the おいている part would usually need to mean "to keep" or "to stock". In other words, both the verb and おいている would have to describe two different and independent actions.

For example, it is simply natural to say:

・～～を買っておいている "to buy ~~ and stock it"

・～～をメモしておいている "to write ~~ down and keep it"