how do I get the Vbox Guest Additions.iso out of where the Synaptic Package stuck it way in a /usr/share/ forgotwhat else

Please provide details:

What is your system setup: What is the operating system running on your hardware, and which operating system do you want to run as guest inside virtualbox?

How did you try installing virtualbox and the virtualbox guest additions - are you using the version provided in the Ubuntu repositories, or is the software downloaded form the virtualbox.org web pages?

Can you start virtualbox?
Is the guest system already installed and running in virtualbox?

Ubuntu 18.04 LTS Newly re installed and I only use Virtual Box for running windows as Sketchup Make 2016 will not run in Ubuntu !
Virtual Box runs as I had an old version of the Guest Additions about 2 versions before one needed to run right . . Synaptic Package Manager goes to the Ubuntu software site and adds Virtual Box version 5.2.18 to the Laptop . . That is OLD version 6, something is the newer one . .I have it running now but it buried the vbox guest additions ISO file way inside of the laptop.. in this directory /usr/share/vbox/ directory and i can't seem to copy or move it . . Synaptic Package manager did this did not install it . . just downloaded and left it there ..

Which version of VirtualBox are you running and from which source?
You have to make sure that the VirtualBox software and the VirtualBox guest additions fit together, i.e. have the same version number.

https://packages.ubuntu.com/bionic-updates/all/virtualbox-guest-additions-iso/filelist shows that the VBoxGuestAdditions.iso file is installed in the directory /usr/share/virtualbox/
If you have installed a certain version of the VirtualBox guest additions with synaptic, then you can also remove it again with the help of synaptic and you should newer try manually moving it around.

There are instructions on https://linuxhint.com/install-sketchup-make-2016-on-linux/ how to install and run Sketchup Make 2016 on Linux with the help of the wine emulator, not requiring a full Windows installation in a virtualized system.
(Disclaimer: I did not try this myself.)

Been there did that and it did not work right . . So went to using Virtual box and it has been working good for years now just lately it has had problems . . version 6.0 Plus has a MAJOR glitch now can't set the number of CPU's to 2 of them and it is really slow So backed up to the one on Ubuntu Software area . .And it takes the Netfix thing to run plus the full install of windows or it does not run plus got a gob of Extension to install to get parts out the other end . . And then there is Arduino IDE for installing Marlin into the 3D prin4rt . . went to 1.8.5 as Geeetech said it works for installing Marlin 1.1.8 into the printer

It lied to you as to what it did with the file . . It just copied the file to that location and it has to be burned to a CD to be loaded into Virtual Box . . Been there did that and the Screen and mouse drivers are not working with out the Guest Additions . . It is why i dumped off a older version to it . . get a tiny screen and mouse will lock up when busy making big part . . I am using something like 5.02 version i had on a CD works and says there is up date . .i just do not trust windows on line

I do not understand why you are talking about problems with VirtualBox version 6.0 Plus.
The Ubuntu repositories for Ubuntu 18.04 have VirtualBox 5.2.18

It seems that you are misunderstanding what to do with the guest additions.
On the host system side the file has to be put into a specific directory (and I assume that is exactly what the installer of the package does), and then you have to activate that version of the guest additions from inside the guest operating system.
There is no need to burn a CD, because the VirtualBox program is able to emulate a CD drive and it can load the disk image that is located in the host directory. You do that with the menu bar entry "Devices - Insert Guest Additions CD image"
see also https://www.smarthomebeginner.com/install-virtualbox-guest-additions-on-windows/

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Like I said it needs to be Installed as the programs says . . That is why it has to be out in the open for burning to the CD it is a ISO file and has to be burned to a CD . . Or you get a small window of windows as the windows driver takes over and that is what you get not FULL SCREEN WINDOWS . . Believe me before the Guest Additions gets installed the Window is like 1/4 of the laptop screen . . The one who wrote that is a windows person not a Linux person and the page is beyond help . . And it says CD means the ISO file is on a CD . . Will not install the ISO file on a computer . . Been There Tried that . .Burning the file to a CD ALWAYS WORKS . .

When running the Windows guest system in virtualbox, does this window have a menu bar with "Machine - View - Devices -..."?
Then you just have to click on "Devices - Install Guest Additions ...".
see also https://docs.oracle.com/cd/E36500_01/E36502/html/qs-guest-additions.html

hahaha well the Synaptic package manager burried it so far away from Where you can get to Except with terminal and that will not let you move it / copy it / expand it it or anything else . . Make a directory on your COMPUTER and let virtual Box go find it . . NEVER GET THERE . . Tried all kinds of ways would not mcopy or mmove file

Here is a link to get the needed file to burn to a CD

https://download.virtualbox.org/virtualbox/5.2.18/

Has the file there as the ISO which can be downloaded

This the reason I deleted 6.0. Plus version of virtual Box and went to the one in the Synaptic Package Software Center . .
. version 6.0 Plus has a MAJOR glitch now can't set the number of CPU's to 2 of t