This video shows the locations for all gems + reward in Luigi's Mansion 2 HD for the Nintendo Switch. Below you can find the timestamps for each level:

00:00 Gloomy Manor A-1
01:11 Gloomy Manor A-2
01:48 Gloomy Manor A-3
02:37 Gloomy Manor A-4
04:07 Gloomy Manor A-5
05:11 Haunted Towers B-1
06:23 Haunted Towers B-2
08:19 Haunted Towers B-3
10:03 Haunted Towers B-4
12:49 Old Clockworks C-1
14:13 Old Clockworks C-2
15:16 Old Clockworks C-3
16:28 Old Clockworks C-5
18:37 Old Clockworks C-Boss
18:49 Secret Mine D-1
21:27 Secret Mine D-2
24:19 Secret Mine D-3
26:48 Treacherous Mansion E-1
28:06 Treacherous Mansion E-2
32:11 Treacherous Mansion E-3
38:05 100% Gems Rewards