From the find options in Maltego, you can search your current graph as well as saved graphs stored on your machine.

Quick Find

The Quick Find option on the investigate tab is a very handy tool to find something specific in a very large graph. The following toolbar will open at the bottom of your graph (the find toolbar can also be opened by clicking Ctrl + F:

You can now enter a search term, select the specific entity type or specify All (the whole graph) and you have the option to search all the Properties, Notes and Detail View. 

Once you click the Find button, the relevant entities will be highlighted in the graph and the search hits will be listed in the Detail View. If you check the Zoom checkbox, then your graph will zoom to your results that match your search criteria.

Find in Files

Find in Files does exactly what the title suggests, it allows you to perform text searches on multiple Maltego graphs that are saved in a specified folder on your machine.

Clicking the Find in Files button open the window shown below:

Under the Where field you can specify the folder that you wish to search. This folder must include .mtgl and/or .mtgx graph files. The Browse button can be used to open a directory window where you can find the folder you wish to search. If the folder that you choose has multiple sub-directories that you also wish to search, then you must check the Recursive checkbox.

The Find input field allows you to specify your search term. The Case Sensitive checkbox can be used to choose whether the search should be case sensitive or not.

The options from the Graph items field will allow you to choose whether to search entities and/or links. It also allows you to limit your search to a specific entity type from the drop down menu.

Finally, the Search in field allows you to choose which of the entities text fields should be searched in.