There are several tools and resources that app developers and marketers can use to find the search volume of keywords in Google:

1. Google Keyword Planner: This is a free tool offered by Google Ads that allows users to research and identify relevant keywords for their business or app. It provides information on the search volume and competition level of different keywords, as well as estimates of the cost-per-click (CPC) for those keywords.
2. Google Trends: This is a free tool offered by Google that allows users to see how often specific keywords are being searched for over time. It provides data on the relative popularity of different keywords and can be used to identify trends and changes in search behavior.
3. Ahrefs: This is a paid keyword research tool that provides a range of data on search volume and competition level for different keywords. It also provides information on the number and quality of backlinks pointing to specific webpages, which can be useful for improving the ranking of an app in search results.
4. SEMrush: This is a paid keyword research tool that provides data on search volume and competition level for different keywords, as well as information on the ranking and performance of specific webpages and apps in search results.

By using these tools and resources, app developers and marketers can research and identify high-quality keywords with a good search volume for their app, which can help improve the app’s ranking in search results and drive user growth.