Can this gun be used on the Tamiya King Tiger?

I'm not sure what you are asking. Do you have an after market barrel you are trying to use?

Yes, which barrel were you trying to fit to the Ktighr?

I mean the Tamiya wm gun for the Tamiya Jagdpanther.

What is a wm gun? Did you mean an aftermarket gun for the Jagdpanther to fit on a king Tiger?

What scale are you working on? By wm do you mean metal?

If the length of the barrel past the mantlet is the same the barrel should work, but there were several barrel configurations.

1:35 and wm is white metal.

A couple of questions.
1. Do you already have the metal barrel or were you thinking of buying one?
2. What companys barrel do you have/want and it's part number.
3. Which King Tiger do you have/want it to go on?

I`m thinking of buying the Tamiya jagdpanther barrel. I have the King Tiger Porsche turret kit no 35169.

I've never seen a white metal gun barrel from Tamiya, only turned aluminium barrels.

The KT kit you are building used the monobloc (one piece) barrel. So, if your WM barrel is also this configuration, then you might be able to make it work.

Link here for reference only!

Most of the early KT's used a one piece barrel:

https://www.ebay.com/itm/1-35-35B20T-RB-MODEL-METAL-BARREL-88mm-for-GERMAN-TIGER-II-PORSCHE-PROMOTE/143242987050?epid=24017950969&hash=item2159f2862a:g:rJYAAOSw-MRbtf2x

There are several other options out there, and say they are for Dragon, but can be made to work on the Tamiya kit. These are a better starting point than a barrel for the JagdPanther.