When reading the kanji pronunciations on renshuu, I understand the commas separate the different pronunciations, but what are the periods/parentheses indicating?
For example,
行 Kunyomi: い.く, ゆ.く, Other times the periods show up in parentheses Kunyomi: い (く)小, ゆ (く)小,
Are these syllables after the period or in parentheses just optional? Or indicate common phrases/usages?
The periods/parentheses do mean the same thing. They are the official stems, or in other words, the hiragana that follows the kanji. So, with the example you gave, いく is written as 行く.
It can also be understood as a way to read the kanji in other forms as well. For example:
楽 - たの.しい
While 楽しい is the "official" listing, the しい can be ripped off and stuck with the verb form 楽しむ.
