In Luke 17:37 who are taken, who are left behind and where are they taken?

Luke 17:37 New King James Version

"And they answered and said to Him, “Where, Lord?” So He said to them, “Wherever the body is, there the eagles will be gathered together.”

Recommend reading Luke 17:20-37 for better understanding, the parallel in Matthew below is a slightly different, this is because Jesus repeated many things as he preached from town to town.

https://www.biblegateway.com/passage/?search=Luke%2017%3A20-37&version=NET;NKJV

Jesus stresses the Necessity for watchfulness-, to keep ready, Jesus explains.

Matthew 24:36-42 (NRSV)

36 “But about that day and hour no one knows, neither the angels of heaven, nor the Son,[a] but only the Father. 37 For as the days of Noah were, so will be the coming of the Son of Man. 38 For as in those days before the flood they were eating and drinking, marrying and giving in marriage, until the day Noah entered the ark, 39 and they knew nothing until the flood came and swept them all away, so too will be the coming of the Son of Man. 40 Then two will be in the field; one will be taken and one will be left. 41 Two women will be grinding meal together; one will be taken and one will be left. 42 Keep awake therefore, for you do not know on what day your Lord is coming.

“Wherever the body is, there the eagles will be gathered together.”

The eagles are farsighted birds , spiritually far sighted individuals are likened to eagles and will be taken along "for salvation" and will gather together where the body is," to the Spiritual Wedding Feast prepared by the King - "God." for His Son Jesus, "The Messiah" (Matthew 22:1-14 NASB)

https://www.biblegateway.com/passage/?search=Matthew+22%3A1-14&version=NET;NKJV

Those abandoned are those who are not spiritually awake, they get consumed in their selfish lifestyle, as did people in Noah's days:" For as in those days before the flood they were eating and drinking, marrying and giving in marriage, until the day Noah entered the ark."( Matthew 24:38 NRSV, Luke 17:26)

Another example given by Jesus ( a few verses earlier) was that of Lot, who was "taken along" by the angel and the others were abandoned.

Luke 17:28-30 NRSV

28 "Likewise, just as it was in the days of Lot: they were eating and drinking, buying and selling, planting and building, 29 but on the day that Lot left Sodom, it rained fire and sulfur from heaven and destroyed all of them 30 —it will be like that on the day that the Son of Man is revealed.

Notes.

Below you will see three different translations of the original Greek Koine. The Greek word "a-e-toi" ( αετοι ) can be translated as "eagles" as well as "vultures," however in terms of context the word "eagles" is by far the better - as in NKJV. To make things worse the NET Bible has added the word "dead" which is not in the Greek text.

ΚΑΤΑ ΛΟΥΚΑΝ 17:37 1881 Westcott-Hort New Testament (WHNU)

37 και αποκριθεντες λεγουσιν αυτω που κυριε ο δε ειπεν αυτοις οπου το σωμα εκει και οι αετοι επισυναχθησονται

Luke 17:37 (NKJV)

37 "And they answered and said to Him, “Where, Lord?” So He said to them, “Wherever the body is, there the eagles will be gathered together"

Luke 17:37 (NET Bible)

37 "Then[a] the disciples[b] said[c] to him, “Where,[d] Lord?” He replied to them, “Where the dead body[e] is, there the vultures will gather.”

Luke 17:37 (NASB)

37 "And answering they *said to Him, “Where, Lord?” And He said to them, “Where the body is, there also the vultures will be gathered.”