I agree that is has to be somewhere in the parish of Rathven. The Cockmuir south of Elgin is in a different county, let alone parish, and the clerk would certainly have noted that if it had been so far away. There are several Cockmuirs in various parts of Scotland (Aberdeenshire, Lanarkshire, West Lothian, Midlothian) besides the one south of Elgin.
I reckon it's possibly the place shown as Blaemuir on the first edition of the Ordnance Survey six-inch map - see
https://maps.nls.uk/geo/explore/#zoom=16&lat=57.6499&lon=-2.9560&layers=5&b=1It's still marked on the modern maps but seems to have been renamed Glen Mor. See
https://www.geograph.org.uk/gridref/NJ4362 and click twice on the map to enlarge it enough.
The 1855 valuation roll lists Blaemuir, proprietor Sir William Gordon of Letterfourie, tenant John Bennet. Some of the archives relating to Gordon of Letterfourie are in the University of Aberdeen archives, and it is possible that they might include for example estate plans showing Blaecockmuir.
The 1851 census shows John Bennet and his wife Isabella Wiseman at Blaemuir.
I can't help with the baptism of James Bennet, but this may be of interest:
https://www.geograph.org.uk/photo/6275125 As might this:
1783, February 9. Thomas Bennet in Walkerdales and Isobel Burges in the parish of Belly were matrimonially contracted consigned pledges and after proclamations were married February 28th. [Rathven Parish Register] This couple had a daughter Helen who married John Russell and had ten of a family in Keith.
The cross just looks like a fancy way of writing 'and'. Are there any more on the same page?