From the Readme:

IMGMOUNT A utility to mount disk images and CD-ROM images in DOSBox. IMGMOUNT DRIVE [imagefile] -t [image_type] -fs [imag […]
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IMGMOUNT
A utility to mount disk images and CD-ROM images in DOSBox.

IMGMOUNT DRIVE [imagefile] -t [image_type] -fs [image_format]
-size [sectorsbytesize, sectorsperhead, heads, cylinders]

imagefile
Location of the image files to mount in DOSBox. The location can
be on a mounted drive inside DOSBox, or on your real disk. It is
possible to mount CD-ROM images (ISOs or CUE/BIN) as well, if you
need CD swapping capabilities specify all images in succession.
The CDs can be swapped with CTRL-F4 at any time.

Even though it only mentions CDs, it is also true for Floppyimages. Something to remember for the next version of Dosbox to correct in the readme, I think.

that was not the problem i have 2 disk directory and i can only mount 1 on every letter. But the thing is that the installation can't switch to the other letter, but for the program there is one floppy and not more. How can i continue my installation.
I dont' use cue or bin Files.

i use
mount a "C:\Duke2\Disk1" -t floppy -ioctl
mount b "C:\Duke2\Disk2" -t floppy -ioctl
mount c "D:\Duke Nukem 2"

As Dominus pointed out, use imgmount:

1) Create images of the diskettes.
2) Mount the 2 diskettes as
imgmount A C:\path\to\image1.img C:\path\to\image2.img -t floppy
3) Swap between the 2 images with CTRL-F4.

Another way to do it :

Mount one directory as a floppy.
Then when the installer asks for Disk 2 erase the mounted "floppy" directory in Windows Explorer
Copy in all files from disk 2 with Windows Explorer.
Then press CTRL-F4.

Continue with installer.

This should work too as I recall.

Erik.

Thank you guys it works

I enjoying Duke Nukem 2 right now 😀