As far as I know bolt action rifles become obsolete after ww2 as automatic guns such as mp-40 or PPSH-1 were invented. So are there any nations that use bolt action rifles similar to the ww2 weapons (say kar98k) today?
Yes. Plenty in fact. Most of them sniper or marksman rifles however.
7.62 Tkiv 85 - Wikipedia - is actually based on WW I & WW II Mosin-Nagant rifles.
However bolt action rifles did not start to be phased out following the adaptation of the submachine guns (like the ones listed). Most of those weapons lacked range and accuracy to be a weapon suitable for all conditions. It was the semi-automatic rifles like M1 Garand (and later the assault rifles) which really meant the end of the bolt action rifles as the main weapon.
why are snipers bolt action? Wouldn’t converting them to be a semi automatic be much faster in taking out targets?
With aimed fire the speed of a bolt action versus an auto is not a material factor. Auto fire is more about suppressive fire.
A sniper may only fire slowly, but has a high probability of a hit; most soldiers have a very low probability of a hit.
Bolt actions, for a given mass, are stronger so can take higher pressures which gives greater range.