Technically you need to specify the isotope of thallium (there are around 40 of them, all but two are unstable, most very unstable).
I'm going to assume you mean Thallium 194, which is it's mass number (it's atomic number is 81).
By alpha emission it will decay into Gold 190 and an alpha particle, if you meant a different isotope of thallium, it will decay into a different isotope of gold (by alpha decay).
When decaying by alpha emission a nucleus drops by 4 in mass number and 2 in atomic number and emits a helium nucleus (alpha particle) which has mass number 4 and atomic number 2.
Notice that the total mass number, and total charge (here only indicated by the atomic numbers ) remains unchanged, just moved around.
If the question meant another isotope, just change the mass numbers accordingly.