What does the suffix gon mean refuring to the shape?

The suffix '---gon' means a 2-dimensional shape. The Word 'polygon', means a shape of many sides.

A 'Trigon' is a shape of three(3) sides, more usually referred to as a 'triangle'.

NB An '-- hedron'. is a 3-dimensional object, such as a 'tetrahedron' ; a 4-sided solid shape.

Although you may wonder were these Words come from. However, if you learn even the most basic of Latin and Classical Greek (Collectively named as 'Classics'), , you will find the roots of these Words in these ancient languages.

NB A lot of modern scientific and mathematical Words come from these ancient languages.

'Mathemetics' ( Classical Greece) means to 'learn'.

'Trigonmetry' ( from above , and Latin) means to 'measure triangles'.