1. Do I shuffle library after 1st search? So it's useless. Elvish Harbinger
2. Is "when you play" old version of ETB? If yes, can I choose both of its abilities? And if I choose second ability. Does this elf add 2 different manas after tap? Quirion Elves
1. When Elvish Harbinger's library resolves, you shuffle your library only if you choose to search it (the "you may" refers to the entirety of actions that follow those two words, including the shuffle; see also this thread). However, if that ability somehow triggers more than once, separate abilities will go on the stack. And you get priority to cast instant spells (such as Opt) before each of them resolves (C.R. 117.1a, 117.4). Thus, after one such ability from Elvish Harbinger resolves, you will eventually get priority to cast spells (such as Opt) that could let you draw the card you put on top of your library this way, if any.
2. Panharmonicon's effect applies only to certain enters-the-battlefield abilities (which generally have the form "When [something] enters the battlefield" or "Whenever [something] enters the battlefield") (see also C.R. 603.1, 603.6a). Neither an ability that starts with "As" (as found in Quirion Elves) nor an ability of the form "When you cast this spell, ..." (as found in Artisan of Kozilek) is an enters-the-battlefield ability (C.R. 603.1, 603.6a), so Panharmonicon doesn't affect either kind of ability. EDIT (Jul. 13, 2020): Note that some cards formerly had the text "[When/whenever] [something] comes into play...". In general, those abilities now read "[When/whenever] [something] enters the battlefield...", which expresses an enters-the-battlefield ability (C.R. 403.5; see also C.R. 603.6a).
1. Do I shuffle library after 1st search? So it's useless. Elvish Harbinger
2. Is "when you play" old version of ETB? If yes, can I choose both of its abilities? And if I choose second ability. Does this elf add 2 different manas after tap? Quirion Elves
2. Panharmonicon's effect applies only to certain enters-the-battlefield abilities (which generally have the form "When [something] enters the battlefield" or "Whenever [something] enters the battlefield") (see also C.R. 603.1, 603.6a). Neither an ability that starts with "As" (as found in Quirion Elves) nor an ability of the form "When you cast this spell, ..." (as found in Artisan of Kozilek) is an enters-the-battlefield ability (C.R. 603.1, 603.6a), so Panharmonicon doesn't affect either kind of ability. EDIT (Jul. 13, 2020): Note that some cards formerly had the text "[When/whenever] [something] comes into play...". In general, those abilities now read "[When/whenever] [something] enters the battlefield...", which expresses an enters-the-battlefield ability (C.R. 403.5; see also C.R. 603.6a).