en.wikipedia.org/wiki/Help:Footnotes#Footnotes:_using_a_source_more_than_once gives the following method:
Definition, anywhere on article, likely ideally as the first usage:
<ref name="myname">{{cite web ...}}</ref>
And then you can use it later on as:
which automatically expands the exact same thing.
<ref name="myname" />
It appears to be impossible to reuse a book reference with different pages with that method however. This is then covered at: en.wikipedia.org/wiki/Wikipedia:Citing_sources#Citing_multiple_pages_of_the_same_source.
To use a different page, see: www.quora.com/On-Wikipedia-how-can-you-cite-the-same-source-more-than-once-without-them-becoming-separate-references/answer/Ciro-Santilli. The best method is:
and then use
<ref name="myname">{{cite web ...}}</ref>
{{p}}
as:
{{p|myname|p=123}}