I wrote an article about how to get the Last Process Date in SSAS Tabular. This is a common request and there are many ways to obtain this information. You can use the metadata provided by XMLA or DMV, just as you can do in SSAS Multidimensional. Or you can use a calculated column that contains the DAX expression NOW() – this might seem an expensive approach, but remember that a column that has the same value for all the rows is absolutely not expensive, because it will be completely compressed in memory!.
I suggest taking a look at the examples in the article, because it is simple to confuse the date of last schema update with the date of last data update, because sometime the schema is updated in an unexpected way…