hi! The origin of a word is called it's "etymology". Any good dictionary will include some etymology (generally, the larger the dictionary, the more detailed the etymology), plus there are some specialist "etymology dictionaries" that focus on just that. One handy online source is the "Online Etymology Dictionary", which has this entry for abracadabra

magical formula, 1690s, from Latin (Q. Severus Sammonicus, 2c.), from Late Greek Abraxas, cabalistic or gnostic name for the supreme god, and thus a word of power. It was written out in a triangle shape and worn around the neck to ward off sickness, etc. Another magical word, from a mid-15c. writing, was ananizapta.

It doesn't have an entry for "alakazam", but the Miriam Webster dictionary has this:

a nonsense word (of obscure origin)

First Known Use: 1937

Also fyi, there's a specialist subreddit, /r/etymology

They are derived from Aramaic/Hebrew, and seem to have origins in antiquity as magical charms or protections. This tradition was continued as many medieval/early-modern cunning men and women believed that these languages had a magical property as well.This belief originated with the use of Hebrew words for divinity like Sabaoth, Adonay or Yhvh for protection from harm or illness which reflected a belief in the power of holy names, so the context of Hebrew phrases used as charms is a bit different in classical antiquity and Christian Europe.

It appears that this belief in the magical property of holy words in Hebrew was extended to other words and phrases which were used as magical charms. Magical healers and conjurers would use random bits of Hebrew, Latin, Greek, Arabic or Syriac for these charms but only a couple of them like abracadabra and alakazam still exist, despite their proliferation in early modern England.