Final answer:
The most reliable evidence of influence on Jack London's writing would be his own autobiographical works. When an author refers to the line "to be or not to be" from Hamlet, it is known as an allusion.
Step-by-step explanation:
In evaluating pieces of evidence regarding the influence on Jack London's writing, the most reliable piece of evidence would typically be primary sources, such as London's own autobiographical works, letters, and diaries, where he may have explicitly stated his influences.
As for the latter part of the question, if an author refers to Shakespeare's line "to be or not to be" from Hamlet, he is using an allusion. An allusion is a brief and indirect reference to a person, place, thing or idea of historical, cultural, literary or political significance without describing them explicitly.