Has Daenerys Targaryen ever learned to wield a weapon so far in ASOIAF?

Dany did have to 'defend' herself from her abusive older brother, and she DID live among the Dothraki for many years. She commanded vast number of highly trained troops - and executed orders again and again as she personally oversaw combat. This constant, heavy exposure to weapons-use, techniques, attacks and defense would certainly ingrain the Dragon Queen with a huge amount of combat and military techniques.

There was an interesting university research study done years ago with "Learning Basketball shooting". One group actually each group was 'shown' basic basketball shooting techniques. Then: one group physically Practiced those techniques, shot baskets, and 'trained' again and again for a period of time. The other group just 'thought' about the skills they were shown for the same amount of time.

Both groups Improved...EXACTLY the SAME amount!!

So, Dany has plenty of exposure - and LOTS of thinking. Moreover, she HAS been shown Fighting in the HBO Series. She 'stood up' to her brother (more than once). She also 'confronted', Trapped - and 'Fought-and-Killed' ALL the Khals of the Dothraki. [As a trained Martial Arts instructor myself - I doubt I could come close to that - even if I was Immune to Fire)! She evaded/avoided their presumed attempts to defend themselves or attack her - while she was Killing them with Fire! That's a formidable example of combat tactics, face-to-face applied strategy and no small degree of skill.

Most poignantly, Dany is show FIGHTING an unending Horde of 'White Walkers' as they assail her and Jorah Mormont. Relentlessly they attack, and Dany evades and avoids each and every assault - coordinating of course with her advisor and friend Jorah (who wields the Valyrian sword: Heartsbane). Dany grabs a weapon too - apparently a 'Dragonglass' blade from a corpse. She defends herself with it - and even Kills one Walker that is attacking Jorah - actually SAVING him (for a few more rounds of combat at least).

Ultimately, she-and-Jorah fend off and kill-off the relentless Wights - buying time for Arya to kill the 'Night King'. While no 'martial expert' per se - Dany is certainly more capable than a sedentary non-combative untrained girl. Further, let us postulate that the 'Targaryen Race' is (apparently) different, more aggressive, more combat-capable than 'regular humans' - as evidenced by their long-military histories and take-over of there entire 'planet' of 'Fire and Ice'. ;)

Not yet... but perhaps she might learn once she returns back to Meereen in the books. Maybe Ser Barristan suggests her to do so, so that she can protect herself in case her guards are not able to stay on her side all the time... and trains her himself.

I have read all of the books and have not noticed any references to her studying armed combat.

I doubt it is something which she will take up because in order to become good enough to really make a difference one needs to train for years (I teach medieval combat so have a bit of an insight) and she simply does not have the time. The books mention how busy she is pretty much every day with her ruling duties.

Also, there is little need for her to fight. She has guards, an army and dragons and no one expects her to lead from the front as a combatant so they do not lose respect for her when she does not. Contrast this to Robert's leadership where his charisma was mainly based on his prowess as a warrior, if he avoided fighting his soldiers would have lost respect - Daenerys does not have this type of relationship with her followers.