You are missing the library that provides MQTTClient.h. Once you've figured out which package provides this library, you can add it as a dependency and link against it.
If there is no package for this library, you will have to add the library as well.
im trying to cross compile a code that include mqttclient.h
i know that i should add the package as a depends in a make file
should i make a new makefile or edit one and add the package?(if ill edit a file then which makefile is it ?)