It may vary depending on the Country Code, but Taxation should happen based on Cumulation WTs such as /102 and /103. Employee's Tax Deductions will be in the /300 series (such as /302 and /303) while Employer's Tax Charges will be in the /400 series.
Tax Calculations should happen while the WTs are still in the Input Table (IT), before they are transfered into the Results Table (RT).
As mentioned by Satish, you can use t-code PC_PAYRESULTS, but if you want to see the Tax Calculations, you should do a Payroll Simulation for one employee, with the "Display log" box checked. Once you have the log on screen, drill down into it until you find the sub-schema where the tax calculations are done (by clicking on the folders one at a time), and then double clicking on the function that does the Tax Calculation (function KATAX and KFTAX in Canada).