In many databases, you should be able to search for scholarly literature which explores the assessment or measurement of various different concepts and variables. Use keywords like assessment, test, scale, indicator, or measurement. It will be relatively easy to find studies which make use of some assessment, test, scale, or measure for the variables in question; in these cases, look at the methodology section of the study to determine what measurements were used, and if they are original or being borrowed from another study.
If the measurement or scale is borrowed, consult the reference list for a full citation and try to track down the original. When looking at an original assessment or scale, look for cues on how the test has been validated for accuracy. Articles where an assessment is introduced or further developed should provide information about the validation process.