In SAP HCM Payroll for SAP S/4HANA, WPBP is both a function and a table. As a function, WPBP (Import work center and basic pay data) is used to transfer master data on the work center and basic pay for the payroll period to internal table WPBP1. The basic pay wage types are stored in the internal table IT1. If all the fields of the table WPBP are the same during the entire payroll period, this table will contain one record1. As a table, WPBP is filled by the infotypes Actions (0000), Organizational Assignment (0001), Planned Working Time (0007), Basic Pay (0008), and Cost Distribution (0027). It contains important organizational and payment-relevant data, and different partial period parameters2.
References = Understanding functions in Payroll Schemas - SAP Community, Internal Tables for Payroll - SAP Help Portal

In SAP HCM Payroll for SAP S/4HANA, the functions that are used to import infotypes data into the current payroll run are WPBP and PIT. The WPBP function is used to transfer master data on the work center and basic pay for the payroll period to the internal table WPBP1. The PIT function is used to import the last previous result for the current period2. References =
https://community.sap.com/t5/enterprise-resource-planning-blogs-by-members/understanding-functions-in-payro
https://help.sap.com/docs/SAP_S4HANA_ON-PREMISE/ff854a903cbf4c10910a5825d787693f/253ec2531b

AMT 0.90: This multiplies the amount of the current wage type by 0.90, effectively reducing it by 10%.
ADDWT*: This adds the reduced wage type amount (along with its number) back to the input table (IT), making it available for subsequent calculations or processing.
Why other options are incorrect:
AMT 0.90 ADDWTI:* The 'I' at the end signifies that the result will be stored in the internal table, but not passed back to the input table (IT) for further processing in the current schema.
AMT 0.10 ADDWT* / AMT 0.10 ADDWTI*:** These would reduce the wage type by only 1%, not
10%.

The internal table ZML (Cumulated Time Wage Types) contains the cumulated time wage types for the current payroll period. It is filled by the function ZLIT (Cumulate Time Wage Types) in the schema XT00 (Time Data Processing). The function ZLIT reads the time wage types from table ZL (Time Wage Types) and cumulates them according to the cumulation class and the cumulation wage type. The cumulation class and the cumulation wage type are defined in table T510S (Time Wage Type Selection). The cumulation class is a grouping of wage types that have the same valuation basis, such as total gross, total net, or total hours. The cumulation wage type is a technical wage type that stores the cumulated amount or number for each cumulation class. For example, the cumulation class 1 (total gross) corresponds to the cumulation wage type
/101, which is stored in table ZML. References =
SAP Help Portal: Internal Tables for Payroll
SAP Help Portal: Time Wage Type Selection
SAP Community: cumulation class, cumulation wage types

When you call up a main schema using transaction PE01, you have the following columns available in the editor:
Line: This column shows the line number of each entry in the schema. It is used to identify and navigate the schema entries.
Function: This column shows the name of the function that is executed by the payroll driver. A function can be a payroll operation, a personnel calculation rule, or a sub-schema. A function can have one or more parameters that define its behavior and output.
Parameter: This column shows the parameters that are passed to the function. Parameters can be constants, variables, or expressions that modify the function's logic or input.Parameters are separated by commas and enclosed in brackets.
Feature: This column shows the name of the feature that is used to determine the value of a parameter. A feature is a decision tree that evaluates certain conditions and returns a value based on the outcome.
Features are used to customize the payroll schema for different scenarios or requirements.
Return Code: This column shows the return code that is generated by the function. A return code is a numerical value that indicates the status or result of the function execution. Return codes can be used to control the flow of the schema or to trigger certain actions.
The columns B. Feature and D. Return Code are not always visible in the editor. They can be displayed or hidden by using the menu options View -> Feature or View -> Return Code. Therefore, they are not correct answers to the question.
References =
SAP Help Portal: Payroll Schema
SAP Community: Understanding functions in Payroll Schemas