We should not confuse the psychological terminology of consciousness, the subconscious and the unconscious with the lay meaning of activities being performed consciously or subconsciously.
The distinction between "conscious" learning and "subconscious" acquisition of linguistic knowledge goes back to the Monitor Model that linguist Stephen Krashen developed in the 1970s and 1980s. According to this theory, human beings develop linguistic skills in two ways: either we
- "subconsciously" acquire knowledge, without realizing that we do so (e.g. by growing up in a certain linguistic environment), or we
- "consciously" learn (e.g. by memorizing lists of words in a foreign language).
Krashen's theory has been both praised and criticized, but this is not the place to go into that debate. It should be enough to note that the hypothesis has as yet not been empirically proven.
From a psychological point of view, learning – of which acquisition is a part, namely that a response to a stimulus has been established – is always not conscious. A conscious activity is one that we are aware of (like intentionally putting a book on a shelf), but learning, that is: the storing of information in the brain, takes place through processes of which we are unaware and in parts of our anatomy over which we have no control.
For example, when you try to memorize a foreign word and its meaning, you cannot consciously put that knowledge in your memory like you can place a book on a shelf. What you must do, for example, is repeat the information until you no longer forget it. But you have no awareness of wether or not the storage was successful. You can only deduce that success from your ability to retrieve the information (i.e. correctly remember). A conscious storage would give you a direct (sensory) feedback of the storage process, similar to how your eyes show you wether or not the book is now on the shelf. If the placing of a book on a shelf worked subconsciously like storing knowledge in your brain, you'd have to retrieve the book from the shelf again to know that it had been put there. Until you took it off the shelf, you couldn't know if it was actually there.
So to answer your question:
For a psychologist, all learning is "subconscious" (but he would not use that word).