Feras Alhlou explains what you can bill clients for. Charge them for project-specific work like competitor research they ask for. Learn industry trends and new tools on your own time, not on their dime.
What expenses should be included in pricing? So anything to do with the client, the project, they specifically ask you to go and research their competitors. All of that I think is valid to be invoiced against the hours that you have, but anything that are more industry specific or you want to acquire more knowledge about the domain of the client or about the tools that they're using, I think that is something that you want to do on your own time, not bill the client for.
