How to determine what encryption is being used a LUKS partition?

If the decrypted volume is /dev/mapper/crypto then you can get the information with

dmsetup table crypto
0 104853504 crypt aes-cbc-essiv:sha256 000[...]000 0 254:2 4096

If the encrypted volume is /dev/storage2/crypto then you get the information with

cryptsetup luksDump /dev/storage2/crypto
LUKS header information for /dev/storage2/crypto

Version:        1
Cipher name:    aes
Cipher mode:    cbc-essiv:sha256
Hash spec:      sha256
[...]

List the disks:

lsblk --fs

Then (used encryption):

cryptsetup luksDump /dev/sdb1

Or (used encryption):

cryptsetup status crypt_sdb1 

In addition (kernel supported encryption and bench):

cat /proc/crypto
ls /lib/modules/$(uname -r)/kernel/crypto/

#cryptsetup benchmark --cipher aes-xts --key-size 256 
cryptsetup benchmark