Again, you answer is a little bit vague and it does not provide any information whatsoever, so therefor you answer will be quite generic.
You can use any Processor you want to extract the data from your source database: GenerateTableFetch+ExecuteSQLRecord, ExecuteSQLRecord, ExecuteSQL, QueryDatabaseTable, QueryDatabaseTableRecord. In all of them you will have to define a DBCP Connection Service so that you can connect to your database. In the processors with Record, you can define the type of the output you will see (Avro, Parquet, JSON, etc)
Afterwards, you do whatever processing you need and assuming that you will use an RestAPI, you can use the InvokeHTTP Processor to call that API Endpoint, with whatever parameters you require. Take note that if those parameters are inside the flowfile, you will need to extract them as attributes, meaning that you will have to add some extra processing.
