Now it works!

$ /usr/local/bin/gnuk-emulation-setup # To generate flash image

From terminal A:

$ /usr/local/libexec/gnuk

From terminal B:

# usbip attach -r 127.0.0.1 -b 1-1

From terminal C:

$ gpg --card-status
Reader ...........: 234B:0000:FSIJ-1.2.5-EMULATED:0
Application ID ...: D276000124010200FFFEF1420A7A0000
Version ..........: 2.0
Manufacturer .....: unmanaged S/N range
Serial number ....: F1420A7A
Name of cardholder: [not set]
Language prefs ...: [not set]
Sex ..............: unspecified
URL of public key : [not set]
Login data .......: [not set]
Signature PIN ....: forced
Key attributes ...: rsa2048 rsa2048 rsa2048
Max. PIN lengths .: 127 127 127
PIN retry counter : 3 3 3
Signature counter : 0
Signature key ....: [none]
Encryption key....: [none]
Authentication key: [none]
General key info..: [none]
$