google says: "A file with the . dat file extension is a generic data file that stores specific information relating to the program that created the file. [...] DAT files typically contain simple text" That is not enough information to recommend a way to read it. Matlab provides many different functions that reads text files. See Importing Data From-Files Programmatically and/or Importing Data from Text Files Interactively
What have you tried?
What is the format of your file? Upload a sample file.
