{!$Context.VariableName} should be used to display Context Variable in Salesforce Einstein BOT.

1. Extract the BOT.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Package xmlns="http://soap.sforce.com/2006/04/metadata">
    <types>
        <members>WhatsApp_Bot</members>
        <name>Bot</name>
    </types>
    <version>59.0</version>
</Package>

2. Add Context Variables to the BOT.

<contextVariables>
	<contextVariableMappings>
		<SObjectType>MessagingSession</SObjectType>
		<fieldName>MessagingSession.ChannelType</fieldName>
		<messageType>WhatsApp</messageType>
	</contextVariableMappings>
	<dataType>Text</dataType>
	<developerName>ChannelType</developerName>
	<label>Channel Type</label>
</contextVariables>
<contextVariables>
	<contextVariableMappings>
		<SObjectType>MessagingSession</SObjectType>
		<fieldName>MessagingSession.ChannelName</fieldName>
		<messageType>WhatsApp</messageType>
	</contextVariableMappings>
	<dataType>Text</dataType>
	<developerName>ChannelName</developerName>
	<label>Channel Name</label>
</contextVariables>

3. Deploy the changes to the org.

4. Make sure the Variables are created in the BOT.

5. Use the format {!$Context.VariableName} to display Context Variable in Salesforce Einstein BOT Builder or Dialog.

Output: