How do I find the electronegetivity of sulphuric acid so that I can determine if its ionic or covalent?

On a piece of paper diagram the structure of H2SO4

Surround the S atom with four 0 atoms, then add two H atoms on the outside of two 0 atoms.

So you have bonding between S and 0 atoms, narrow difference in electronegativity - covalent bonding

and bonding between H and 0 atoms, also a difference of electronegativity low enough to be considered basically covalently bonded. Overall, a covalently bonded molecule.