I've not worked directly in this area but am broadly familiar with it.
The core part of the business is working to complete tax returns for employees who are working internationally. Most of the tax returns are done offshore but often time will be spent reviewing them and doing any of the more complex, or ones for particularly senior people.
Normally you'd hold a short call with the employee to talk them through the tax implications of their move and offer any advice (e.g. max no of days to spend in a country). New grads will normally sit in on these. Probably towards the end of your first year you'll do calls on your own with junior employees.
As well as this, the client may request you to look at a specific employee's arrangement or provide tax advice on any number of hypothetical situations (e.g. closing an overseas office and paying redundancy). In these cases you'll probably have to do some calculations, look at the employee's recent tax returns, possibly speak with them, and draft a short document - often just an email - outlining the position. Sometimes larger bits of ad hoc advice may come up of course.
Often, new grads can find themselves doing lots of non technical work to support larger accounts - so be prepared for this. It could be managing the billing, owning trackers showing the status of employee's returns, gathering and managing all the data that comes in from employees and generally making sure that EY delivers what it says it will to the client.
I'm sure there are lots of other things they do too - tax implications for different pensions, benefits, bonus plans etc. There may be some research - e.g. what are the tax laws in a certain country for a specific thing..but I wouldn't expect loads of research. 90% of the work will have been seen before.
Be aware that this is a tax role in quite a niche area and doesn't have many similarities with consulting.