In addition to the great answers above, if I already have a reference ID, I usually just put it straight into the address bar. Eg.: suttacentral.net/an4.192.
If I already know the text I want to get to (ie. Bhante Sujato’s, or Ven. Thanissaro’s, English translation, or whatever else), I save myself one more click by adding that to the address bar: https://suttacentral.net/an4.192/en/thanissaro.
Just to go back a step, though, looking at the references given in the OP, I’m a bit confused as to what the first part of the references actually refer to. Very often, page numbers will be Pali Text Society (PTS) references, which you can view on the sutta card:
You can also view PTS (and others where applicable) references when reading a sutta by selecting to display “information such as volume/page references, variant readings, etc.” under the text settings.
Taking the first example from the OP:
A. pg 121, 4:192
Seeing that the “A. pg 121” isn’t the PTS reference for an4.192 (as per the image above), I wondered if this was maybe the page number in Bhikkhu Bodhi’s translation… but, nope (it’s pg 563 there). In turn, might I ask, where is the pg121 coming from?
Assuredly, sutta referencing systems are profoundly puzzling! I kind of think my chances of becoming fully awakened at some point in some life are actually a little higher than my ever fully comprehending all the numbering systems.
Have you tried treating the second part as a PTS number. The last reference in your list especially (that uses Roman numerals), made me wonder if they might be PTS numbers, although funnily enough, that particular reference definitely can’t be a PTS ref as the AN was printed in full over five books (in PTS refs the first number corresponds to the volume, and the second number the relevant page in that volume).
For speed, I use a text file to look these things up, but a PTS converter found at http://pts.ticao.de/ is an excellent tool for finding PTS references on SC.
Treating your referrences in this way you’d end up with
PTS > SC conversion
A. pg 121, 4:192
A. pg 75 3:100;
pg 168 6:55
D. pg 102-103; 2:76-79
A. pg 165; VI:47
Obviously, it’s doesn’t answer to everything perfectly, but thought I’d just mention it to see if you’re able to match up some of the quotes in this way.
The one other thought that I had about the first page numbers is that maybe they could possibly refer to the page numbers of Bhikkhu Bodhi’s In the Buddha’s Words: An Anthology of Discourses from the Pali Canon.
Without more evidence to go on, I’m not sure how else to try and tackle the mystery, but suffice to say, whoever compiled the slideshow, has embraced a rather funky approach to referencing. What are the actual quotes corresponding to these references?