Try "apt search libsomething" in the terminal. Or install a graphical package manager like synaptic.

I prefer Synaptic compared to all the other fancy managers.

Im having an error with Trine..

libz.so.1 version "ZLIB.1.2.9" not found (required by /usr/lib/i386-Linux-gnu/libpng16.so.16) 

If I look for libz.so.1 on synaptic, there is no result..

You can find the packages including that file here:
https://packages.ubuntu.com/search?suite=bionic&arch=i386&mode=exactfilename&searchon=contents&keywords=libz.so.1

Ubuntu 18.04 uses zlib 1.2.11, so you're probably having a conflict between the libraries in your system and older versions shipped with Trine. I would try to delete some of the libraries included with Trine, starting with libpng16 (if present).

Libpng16 is present in Ubuntu 18.04, Robert's advice is your best starting point. I've had a similar issue with other games and removing some bundled libs fixed it.

Quoting: Comandante ÑoñardoIm having an error with Trine..

libz.so.1 version "ZLIB.1.2.9" not found (required by /usr/lib/i386-Linux-gnu/libpng16.so.16) 

If I look for libz.so.1 on synaptic, there is no result..

In Ubuntu repo the zlib package is called "zlib1g" search for that in Synaptic. Most likely the system only came with 64bit library preinstalled. The 32bit one can be found as "zlib1g:i386" and you have to install that manually.

Thanks for the tips... Deleting the Trine Zlib make the game launcher load, but when I click start, it throw me another error related with some Murrine thing... I installed the 32 bit version of Gtk2-engines-murrine from the site You mentioned... Now I have some Pixmap error... I installed the Pixmap package, but I still having the same pixmap error...

Deleting all the Trine libraries throw an error about some missing libpng12...

After A LOT of trial and errors (including the Install of the windows version via wine and the Linux version of the Humble edition of Trine... and I jump to the conclusion that the only old library needed in the Trine lib folder is the file libpng12.so.0.50.0 and a symlink to it called libpng12.so.0

I know you write that you've solved the problem, but honestly theese command are something that anyone unfortunate enough to ever be confronted with the existence of .so files should know ;)

so for future reference:

To find out what (installed) package owns a file:

dpkg -S file

Since you are missing it, it obviously wont be installed so you will need apt-file

apt-file search file

For some reason this nifty tool is not a part of most apt based distros, so you will need to install and update it first:
apt install apt-file
apt-file update