rightwriter,
“What symbol/icon in Judaism symbolizes/represents Judaism the most?”
This is a subjective question. I think most people today would most associate the 6-sided “magen David” star with Judaism, though on the scale of Jewish history, it’s a fairly recent association. The seven branched menorah from the beis hamikdash probably represents Judaism the most.
“What customs in our religion have any skeptical/unclear origins? Are there any customs which Judaism adopted from other religions or are they undoubtedly Jewish origins(red string,blue eye etc.)?”
That depends on how you define “our religion” and “Judaism.” Also, I am an Orthodox Jew and interact with many other Orthodox Jews, and the “red string” and “blue eye” are not things that I encounter or think about.
“Did all religions originate from or originally based on Judaism? Is there any wisdom in other religions that may have been forgotten in Judaism such as the “matanos” that were given to Hagar on her departure?”
No. Idolatrous religions were all made up by people. Christianity and Islam did derive some of their ideas from Judaism. As far as wisdom in other religions, Jews are strictly forbidden from investigating other religions and their practices.
“Why isn’t Judaism the most ancient of all religions if it is the correct one or is it the most ancient just wasn’t officially considered a religion?”
Judaism was designed for Jews, the nation of descendants of Avraham, Yitzchak, and Yaakov who were slaves in Egypt and taken out of there by Hashem, and righteous converts who join that nation. The building blocks of Judaism (e.g., Torah) were in the world since it was created.
“What’s with Sefer raziel hamalach? Any thoughts?”
None from me.