How to predict ease of oxidation or reduction for a given oxidising or reducing agent?
This goes to the heart of organic chemistry and most of it is just about learning the properties of the most common reagents, then understanding where to find the detailed information. A good Organic chemistry text book is the starting point, then there are lists to help, for examples list of oxidising agents, list of reducing agents or entire series of books on Organic chemistry reagents e.g. Fieser &amp; Fieser which a good library should have. For individual transformations databases such as Reaxys or Scifinder are searchable by structure and can find the conditions under which a transformation has previously been done. If the transformation has not previously been reported then you have to use your judgement as to which conditions to try, that is where the real art of synthesis comes in. It is important to note that solvent and temperature play a huge role in such transformations. Reactions that proceed in one solvent may give a different outcome in another.

Dibal-H does reduce carboxylic acids, but require multiple equivalents and elevated temperature or additional reagents such as TMSiCl paper here