Taking this sentence as an example:
納入した学費は、理由の如何{を問わず/に関わらず}返却しません。
I always have a hard time knowing how to read 如何; いか, いかが, even どう or いかん sometimes..
I've checked if the question was answered previously, I hope I didn't missed it!
In the sentence you gave it is functioning as a noun, so its reading is [如何]{いかん}.
❶[名]事の次第。なりゆき。ようす。「理由の―によっては」「事の成否は君の協力―による」
Source: デジタル大辞泉
Recognizing from context the part of speech 如何 is functioning as (noun, adverb, adjectival verb) is helpful as a first step. Also, recognizing if it is part of a set phrase e.g. [如何]{どう}あっても, [如何]{どう}致しまして, [如何]{いかが}なものか, [如何]{いかん}せん, [如何]{いか}に should get you there in most cases.