In simple terms we can say IoT is a system of things integrated with sensors, software's, electronics which are connected to each other & can exchange data or Information with other connected devices.
so the main key skills to be focus to become an IoT engineer are below.
a)knowledge on physical hardware like microprocessors, gateways, sensors, etc. : hardware engineering, degree in electronics and electrical, knowledge on communication protocols, sensors, microprocessors etc. will help to reach the goal of IoT engineer.
b)Programming the devices and platforms. : programming languages like python, c++, node js etc is few ones which will take you the right path.
c)cloud and other server administration: cloud AWS, azure , data analytics, cyber security etc is really required to understand how the data is utilized.
d) user interface involves front end page development: languages like php, html, for developing front end user interface.
I understand it will look too much to take to become an IoT engineer, you may b e thinking how one person can develop knowledge all these skills. you don’t need to do everything together. start small, with basic hardware and electronics, do some small projects. then can upgrade skills to each next section.
learn the basic using Raspberry Pi and Arduino, simple IoT projects. Refer below for some samples.