Question

How to represent protonation in an equation?

Answer 1

protonation means addition of proton in a atom , molecule ,or ion form a conjugate acid.
protonation of water by H2SO4
H2SO4  +  H2O   ------------------>    H3O+     +    HSO4-
protonation of isobutene in the formation of carbocation 
(CH3)2C=CH2   +   HBF4  -------------------->    (CH3)3C+        +      BF4-
for representation make a arrow in the direction of flow of electron .
electron flow from an atom which have lone pair or a molecule which have double bond or triple bond or in the molecule from an atom which have a lone pair .